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 $93.30   3.537%   $96.6   $96.60   $96.60   $96.60  
  Purchase #2 $36.36   6.170%   $38.6034   $38.60   $38.60   $38.60  
  Purchase #3 $86.26   11.714%   $96.3645   $96.36   $96.35   $96.40  
  Purchase #4 $68.95   3.130%   $71.1081   $71.11   $71.10   $71.10  
  Purchase #5 $101.95   11.762%   $113.9414   $113.94   $113.95   $113.90  
  Purchase #6 $229.80   12.503%   $258.5319   $258.53   $258.55   $258.50  
  Purchase #7 $20.33   4.871%   $21.3203   $21.32   $21.30   $21.30  
  7 purchase totals = $636.95       $696.4696   $696.46   $696.45   $696.40