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 $183.70   8.109%   $198.5962   $198.60   $198.60   $198.60  
  Purchase #2 $213.71   5.672%   $225.8316   $225.83   $225.85   $225.80  
  Purchase #3 $133.69   9.505%   $146.3972   $146.40   $146.40   $146.40  
  Purchase #4 $141.76   10.506%   $156.6533   $156.65   $156.65   $156.70  
  Purchase #5 $147.60   6.344%   $156.9637   $156.96   $156.95   $157.00  
  Purchase #6 $88.91   4.208%   $92.6513   $92.65   $92.65   $92.70  
  Purchase #7 $45.97   3.332%   $47.5017   $47.50   $47.50   $47.50  
  7 purchase totals = $955.34       $1,024.5950   $1,024.59   $1,024.60   $1,024.70