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 $195.59   10.540%   $216.2052   $216.21   $216.20   $216.20  
  Purchase #2 $157.38   6.419%   $167.4822   $167.48   $167.50   $167.50  
  Purchase #3 $235.69   4.220%   $245.6361   $245.64   $245.65   $245.60  
  Purchase #4 $210.44   6.772%   $224.691   $224.69   $224.70   $224.70  
  Purchase #5 $116.35   9.764%   $127.7104   $127.71   $127.70   $127.70  
  Purchase #6 $157.25   8.499%   $170.6147   $170.61   $170.60   $170.60  
  Purchase #7 $45.90   9.507%   $50.2637   $50.26   $50.25   $50.30  
  7 purchase totals = $1,118.60       $1,202.6033   $1,202.60   $1,202.60   $1,202.60