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 $201.83   12.114%   $226.2797   $226.28   $226.30   $226.30  
  Purchase #2 $204.61   10.204%   $225.4884   $225.49   $225.50   $225.50  
  Purchase #3 $69.33   5.346%   $73.0364   $73.04   $73.05   $73.00  
  Purchase #4 $45.58   8.729%   $49.5587   $49.56   $49.55   $49.60  
  Purchase #5 $23.49   10.845%   $26.0375   $26.04   $26.05   $26.00  
  Purchase #6 $203.34   7.505%   $218.6007   $218.60   $218.60   $218.60  
  Purchase #7 $179.43   9.790%   $196.9962   $197.00   $197.00   $197.00  
  7 purchase totals = $927.61       $1,015.9976   $1,016.01   $1,016.05   $1,016.00