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 $235.31   13.572%   $267.2463   $267.25   $267.25   $267.20  
  Purchase #2 $139.78   7.316%   $150.0063   $150.01   $150.00   $150.00  
  Purchase #3 $242.77   5.182%   $255.3503   $255.35   $255.35   $255.40  
  Purchase #4 $61.37   5.443%   $64.7104   $64.71   $64.70   $64.70  
  Purchase #5 $25.90   6.820%   $27.6664   $27.67   $27.65   $27.70  
  Purchase #6 $123.98   9.550%   $135.8201   $135.82   $135.80   $135.80  
  Purchase #7 $200.62   12.722%   $226.1429   $226.14   $226.15   $226.10  
  7 purchase totals = $1,029.73       $1,126.9427   $1,126.95   $1,126.90   $1,126.90