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 $229.90   5.233%   $241.9307   $241.93   $241.95   $241.90  
  Purchase #2 $67.57   6.632%   $72.0512   $72.05   $72.05   $72.10  
  Purchase #3 $160.40   8.346%   $173.787   $173.79   $173.80   $173.80  
  Purchase #4 $99.65   5.534%   $105.1646   $105.16   $105.15   $105.20  
  Purchase #5 $168.27   6.497%   $179.2025   $179.20   $179.20   $179.20  
  Purchase #6 $43.75   11.175%   $48.6391   $48.64   $48.65   $48.60  
  Purchase #7 $182.53   10.188%   $201.1262   $201.13   $201.15   $201.10  
  7 purchase totals = $952.07       $1,021.9013   $1,021.90   $1,021.95   $1,021.90