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 $48.86   12.463%   $54.9494   $54.95   $54.95   $54.90  
  Purchase #2 $56.35   10.455%   $62.2414   $62.24   $62.25   $62.20  
  Purchase #3 $151.98   13.778%   $172.9198   $172.92   $172.90   $172.90  
  Purchase #4 $16.67   11.743%   $18.6276   $18.63   $18.65   $18.60  
  Purchase #5 $20.86   12.390%   $23.4446   $23.44   $23.45   $23.40  
  Purchase #6 $241.48   10.641%   $267.1759   $267.18   $267.20   $267.20  
  Purchase #7 $160.84   4.324%   $167.7947   $167.79   $167.80   $167.80  
  7 purchase totals = $697.04       $767.1534   $767.15   $767.20   $767.00