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 $151.31   11.689%   $168.9966   $169.00   $169.00   $169.00  
  Purchase #2 $118.27   13.732%   $134.5108   $134.51   $134.50   $134.50  
  Purchase #3 $82.92   7.252%   $88.9334   $88.93   $88.95   $88.90  
  Purchase #4 $104.31   8.529%   $113.2066   $113.21   $113.20   $113.20  
  Purchase #5 $49.95   11.199%   $55.5439   $55.54   $55.55   $55.50  
  Purchase #6 $222.94   9.558%   $244.2486   $244.25   $244.25   $244.20  
  Purchase #7 $77.46   12.712%   $87.3067   $87.31   $87.30   $87.30  
  7 purchase totals = $807.16       $892.7466   $892.75   $892.75   $892.60