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 $128.59   4.819%   $134.7868   $134.79   $134.80   $134.80  
  Purchase #2 $15.69   3.603%   $16.2553   $16.26   $16.25   $16.30  
  Purchase #3 $205.39   3.655%   $212.897   $212.90   $212.90   $212.90  
  Purchase #4 $246.46   10.195%   $271.5866   $271.59   $271.60   $271.60  
  Purchase #5 $225.34   5.728%   $238.2475   $238.25   $238.25   $238.20  
  Purchase #6 $51.90   3.703%   $53.8219   $53.82   $53.80   $53.80  
  Purchase #7 $119.89   13.428%   $135.9888   $135.99   $136.00   $136.00  
  7 purchase totals = $993.26       $1,063.5839   $1,063.60   $1,063.60   $1,063.60