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 $61.56   9.620%   $67.4821   $67.48   $67.50   $67.50  
  Purchase #2 $124.27   7.547%   $133.6487   $133.65   $133.65   $133.60  
  Purchase #3 $42.77   12.414%   $48.0795   $48.08   $48.10   $48.10  
  Purchase #4 $217.80   12.383%   $244.7702   $244.77   $244.75   $244.80  
  Purchase #5 $150.40   7.254%   $161.31   $161.31   $161.30   $161.30  
  Purchase #6 $20.83   10.814%   $23.0826   $23.08   $23.10   $23.10  
  Purchase #7 $74.97   9.388%   $82.0082   $82.01   $82.00   $82.00  
  7 purchase totals = $692.60       $760.3813   $760.38   $760.40   $760.40