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 $60.86   11.120%   $67.6276   $67.63   $67.65   $67.60  
  Purchase #2 $40.63   9.664%   $44.5565   $44.56   $44.55   $44.60  
  Purchase #3 $122.96   9.462%   $134.5945   $134.59   $134.60   $134.60  
  Purchase #4 $109.79   7.130%   $117.618   $117.62   $117.60   $117.60  
  Purchase #5 $57.88   4.676%   $60.5865   $60.59   $60.60   $60.60  
  Purchase #6 $54.95   11.663%   $61.3588   $61.36   $61.35   $61.40  
  Purchase #7 $129.90   11.839%   $145.2789   $145.28   $145.30   $145.30  
  7 purchase totals = $576.97       $631.6208   $631.63   $631.65   $631.70