Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $113.64   8.729%   $123.5596   $123.56   $123.55   $123.60  
  Purchase #2 $236.94   13.631%   $269.2373   $269.24   $269.25   $269.20  
  Purchase #3 $223.85   6.162%   $237.6436   $237.64   $237.65   $237.60  
  Purchase #4 $202.88   11.166%   $225.5336   $225.53   $225.55   $225.50  
  Purchase #5 $139.87   4.139%   $145.6592   $145.66   $145.65   $145.70  
  Purchase #6 $136.50   12.434%   $153.4724   $153.47   $153.45   $153.50  
  Purchase #7 $249.49   3.601%   $258.4741   $258.47   $258.45   $258.50  
  7 purchase totals = $1,303.17       $1,413.5798   $1,413.57   $1,413.55   $1,413.60