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 $169.31   12.772%   $190.9343   $190.93   $190.95   $190.90  
  Purchase #2 $52.34   11.832%   $58.5329   $58.53   $58.55   $58.50  
  Purchase #3 $247.59   10.526%   $273.6513   $273.65   $273.65   $273.70  
  Purchase #4 $41.97   7.245%   $45.0107   $45.01   $45.00   $45.00  
  Purchase #5 $107.43   13.118%   $121.5227   $121.52   $121.50   $121.50  
  Purchase #6 $242.80   12.828%   $273.9464   $273.95   $273.95   $273.90  
  Purchase #7 $25.80   12.428%   $29.0064   $29.01   $29.00   $29.00  
  7 purchase totals = $887.24       $992.6047   $992.60   $992.60   $992.50