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 $91.66   6.822%   $97.913   $97.91   $97.90   $97.90  
  Purchase #2 $137.49   7.397%   $147.6601   $147.66   $147.65   $147.70  
  Purchase #3 $68.62   9.596%   $75.2048   $75.20   $75.20   $75.20  
  Purchase #4 $64.80   5.412%   $68.307   $68.31   $68.30   $68.30  
  Purchase #5 $25.98   12.225%   $29.1561   $29.16   $29.15   $29.20  
  Purchase #6 $64.31   11.125%   $71.4645   $71.46   $71.45   $71.50  
  Purchase #7 $248.87   3.212%   $256.8637   $256.86   $256.85   $256.90  
  7 purchase totals = $701.73       $746.5692   $746.56   $746.50   $746.70