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 $90.38   13.556%   $102.6319   $102.63   $102.65   $102.60  
  Purchase #2 $95.25   11.873%   $106.559   $106.56   $106.55   $106.60  
  Purchase #3 $202.64   11.511%   $225.9659   $225.97   $225.95   $226.00  
  Purchase #4 $245.74   9.773%   $269.7562   $269.76   $269.75   $269.80  
  Purchase #5 $248.71   6.749%   $265.4954   $265.50   $265.50   $265.50  
  Purchase #6 $38.77   6.220%   $41.1815   $41.18   $41.20   $41.20  
  Purchase #7 $172.88   8.153%   $186.9749   $186.97   $186.95   $187.00  
  7 purchase totals = $1,094.37       $1,198.5648   $1,198.57   $1,198.55   $1,198.70