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 $54.58   13.766%   $62.0935   $62.09   $62.10   $62.10  
  Purchase #2 $218.88   11.169%   $243.3267   $243.33   $243.35   $243.30  
  Purchase #3 $184.62   5.858%   $195.435   $195.44   $195.45   $195.40  
  Purchase #4 $245.63   12.505%   $276.346   $276.35   $276.35   $276.30  
  Purchase #5 $16.39   7.474%   $17.615   $17.62   $17.60   $17.60  
  Purchase #6 $122.29   5.744%   $129.3143   $129.31   $129.30   $129.30  
  Purchase #7 $112.72   6.591%   $120.1494   $120.15   $120.15   $120.10  
  7 purchase totals = $955.11       $1,044.2799   $1,044.29   $1,044.30   $1,044.10