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 $68.35   3.782%   $70.935   $70.94   $70.95   $70.90  
  Purchase #2 $204.53   5.337%   $215.4458   $215.45   $215.45   $215.40  
  Purchase #3 $144.56   9.834%   $158.776   $158.78   $158.80   $158.80  
  Purchase #4 $14.79   6.349%   $15.729   $15.73   $15.75   $15.70  
  Purchase #5 $62.75   11.719%   $70.1037   $70.10   $70.10   $70.10  
  Purchase #6 $76.26   12.736%   $85.9725   $85.97   $85.95   $86.00  
  Purchase #7 $128.68   5.304%   $135.5052   $135.51   $135.50   $135.50  
  7 purchase totals = $699.92       $752.4672   $752.48   $752.50   $752.40