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 $50.58   3.114%   $52.1551   $52.16   $52.15   $52.20  
  Purchase #2 $159.97   6.644%   $170.5984   $170.60   $170.60   $170.60  
  Purchase #3 $236.78   6.323%   $251.7516   $251.75   $251.75   $251.80  
  Purchase #4 $131.94   9.526%   $144.5086   $144.51   $144.50   $144.50  
  Purchase #5 $201.45   8.440%   $218.4524   $218.45   $218.45   $218.50  
  Purchase #6 $26.28   11.270%   $29.2418   $29.24   $29.25   $29.20  
  Purchase #7 $89.29   3.203%   $92.15   $92.15   $92.15   $92.20  
  7 purchase totals = $896.29       $958.8579   $958.86   $958.85   $959.00