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 $173.34   12.349%   $194.7458   $194.75   $194.75   $194.70  
  Purchase #2 $54.55   6.838%   $58.2801   $58.28   $58.30   $58.30  
  Purchase #3 $207.44   11.412%   $231.1131   $231.11   $231.10   $231.10  
  Purchase #4 $244.93   12.513%   $275.5781   $275.58   $275.60   $275.60  
  Purchase #5 $89.92   8.727%   $97.7673   $97.77   $97.75   $97.80  
  Purchase #6 $160.69   5.762%   $169.949   $169.95   $169.95   $169.90  
  Purchase #7 $64.97   6.645%   $69.2873   $69.29   $69.30   $69.30  
  7 purchase totals = $995.84       $1,096.7207   $1,096.73   $1,096.75   $1,096.70