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 $116.53   7.195%   $124.9143   $124.91   $124.90   $124.90  
  Purchase #2 $241.96   6.373%   $257.3801   $257.38   $257.40   $257.40  
  Purchase #3 $69.36   12.523%   $78.046   $78.05   $78.05   $78.00  
  Purchase #4 $151.60   4.532%   $158.4705   $158.47   $158.45   $158.50  
  Purchase #5 $43.37   13.417%   $49.189   $49.19   $49.20   $49.20  
  Purchase #6 $184.41   4.731%   $193.1344   $193.13   $193.15   $193.10  
  Purchase #7 $137.83   9.480%   $150.8963   $150.90   $150.90   $150.90  
  7 purchase totals = $945.06       $1,012.0306   $1,012.03   $1,012.05   $1,012.00