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 $68.30   9.811%   $75.0009   $75.00   $75.00   $75.00  
  Purchase #2 $130.92   3.570%   $135.5938   $135.59   $135.60   $135.60  
  Purchase #3 $120.42   13.806%   $137.0452   $137.05   $137.05   $137.00  
  Purchase #4 $169.38   11.477%   $188.8197   $188.82   $188.80   $188.80  
  Purchase #5 $36.69   10.650%   $40.5975   $40.60   $40.60   $40.60  
  Purchase #6 $119.89   3.342%   $123.8967   $123.90   $123.90   $123.90  
  Purchase #7 $200.98   12.581%   $226.2653   $226.27   $226.25   $226.30  
  7 purchase totals = $846.58       $927.2191   $927.23   $927.20   $927.20