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 $122.67   8.152%   $132.6701   $132.67   $132.65   $132.70  
  Purchase #2 $55.99   13.287%   $63.4294   $63.43   $63.45   $63.40  
  Purchase #3 $67.76   12.464%   $76.2056   $76.21   $76.20   $76.20  
  Purchase #4 $120.56   9.389%   $131.8794   $131.88   $131.90   $131.90  
  Purchase #5 $118.32   5.501%   $124.8288   $124.83   $124.85   $124.80  
  Purchase #6 $209.28   8.508%   $227.0855   $227.09   $227.10   $227.10  
  Purchase #7 $10.78   12.699%   $12.149   $12.15   $12.15   $12.10  
  7 purchase totals = $705.36       $768.2478   $768.26   $768.30   $768.20