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 $92.60   6.419%   $98.544   $98.54   $98.55   $98.50  
  Purchase #2 $11.49   9.765%   $12.612   $12.61   $12.60   $12.60  
  Purchase #3 $20.92   5.556%   $22.0823   $22.08   $22.10   $22.10  
  Purchase #4 $209.26   10.814%   $231.8894   $231.89   $231.90   $231.90  
  Purchase #5 $118.55   6.839%   $126.6576   $126.66   $126.65   $126.70  
  Purchase #6 $101.92   5.519%   $107.545   $107.55   $107.55   $107.50  
  Purchase #7 $32.28   4.153%   $33.6206   $33.62   $33.60   $33.60  
  7 purchase totals = $587.02       $632.9509   $632.95   $632.95   $632.90