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 $88.58   6.622%   $94.4458   $94.45   $94.45   $94.40  
  Purchase #2 $231.27   13.707%   $262.9702   $262.97   $262.95   $263.00  
  Purchase #3 $63.44   3.327%   $65.5506   $65.55   $65.55   $65.60  
  Purchase #4 $98.38   5.592%   $103.8814   $103.88   $103.90   $103.90  
  Purchase #5 $156.30   4.457%   $163.2663   $163.27   $163.25   $163.30  
  Purchase #6 $141.31   6.320%   $150.2408   $150.24   $150.25   $150.20  
  Purchase #7 $118.79   7.694%   $127.9297   $127.93   $127.95   $127.90  
  7 purchase totals = $898.07       $968.2848   $968.29   $968.30   $968.30