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 $41.93   3.374%   $43.3447   $43.34   $43.35   $43.30  
  Purchase #2 $232.61   3.790%   $241.4259   $241.43   $241.45   $241.40  
  Purchase #3 $201.28   12.652%   $226.7459   $226.75   $226.75   $226.70  
  Purchase #4 $65.46   11.136%   $72.7496   $72.75   $72.75   $72.70  
  Purchase #5 $91.61   8.743%   $99.6195   $99.62   $99.60   $99.60  
  Purchase #6 $25.95   13.788%   $29.528   $29.53   $29.55   $29.50  
  Purchase #7 $202.74   12.670%   $228.4272   $228.43   $228.45   $228.40  
  7 purchase totals = $861.58       $941.8408   $941.85   $941.90   $941.60