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 $193.79   8.729%   $210.7059   $210.71   $210.70   $210.70  
  Purchase #2 $100.92   8.624%   $109.6233   $109.62   $109.60   $109.60  
  Purchase #3 $83.47   8.318%   $90.413   $90.41   $90.40   $90.40  
  Purchase #4 $148.65   8.773%   $161.6911   $161.69   $161.70   $161.70  
  Purchase #5 $63.37   6.112%   $67.2432   $67.24   $67.25   $67.20  
  Purchase #6 $112.62   3.225%   $116.252   $116.25   $116.25   $116.30  
  Purchase #7 $241.86   10.573%   $267.4319   $267.43   $267.45   $267.40  
  7 purchase totals = $944.68       $1,023.3604   $1,023.35   $1,023.35   $1,023.30