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 $76.59   10.483%   $84.6189   $84.62   $84.60   $84.60  
  Purchase #2 $126.38   4.573%   $132.1594   $132.16   $132.15   $132.20  
  Purchase #3 $72.58   10.174%   $79.9643   $79.96   $79.95   $80.00  
  Purchase #4 $197.40   13.495%   $224.0391   $224.04   $224.05   $224.00  
  Purchase #5 $200.54   5.104%   $210.7756   $210.78   $210.80   $210.80  
  Purchase #6 $250.74   4.531%   $262.101   $262.10   $262.10   $262.10  
  Purchase #7 $117.35   7.147%   $125.737   $125.74   $125.75   $125.70  
  7 purchase totals = $1,041.58       $1,119.3953   $1,119.40   $1,119.40   $1,119.40