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 $88.86   4.620%   $92.9653   $92.97   $92.95   $93.00  
  Purchase #2 $139.43   13.777%   $158.6393   $158.64   $158.65   $158.60  
  Purchase #3 $105.68   8.370%   $114.5254   $114.53   $114.55   $114.50  
  Purchase #4 $101.50   5.594%   $107.1779   $107.18   $107.20   $107.20  
  Purchase #5 $17.78   10.165%   $19.5873   $19.59   $19.60   $19.60  
  Purchase #6 $120.95   13.542%   $137.329   $137.33   $137.35   $137.30  
  Purchase #7 $208.68   4.547%   $218.1687   $218.17   $218.15   $218.20  
  7 purchase totals = $782.88       $848.3929   $848.41   $848.45   $848.40