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 $67.68   13.717%   $76.9637   $76.96   $76.95   $77.00  
  Purchase #2 $37.36   7.440%   $40.1396   $40.14   $40.15   $40.10  
  Purchase #3 $228.56   10.699%   $253.0136   $253.01   $253.00   $253.00  
  Purchase #4 $239.55   3.507%   $247.951   $247.95   $247.95   $248.00  
  Purchase #5 $45.59   12.813%   $51.4314   $51.43   $51.45   $51.40  
  Purchase #6 $227.96   5.364%   $240.1878   $240.19   $240.20   $240.20  
  Purchase #7 $36.32   13.481%   $41.2163   $41.22   $41.20   $41.20  
  7 purchase totals = $883.02       $950.9034   $950.90   $950.90   $950.90