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 $162.69   12.236%   $182.5967   $182.60   $182.60   $182.60  
  Purchase #2 $247.34   10.815%   $274.0898   $274.09   $274.10   $274.10  
  Purchase #3 $14.94   6.646%   $15.9329   $15.93   $15.95   $15.90  
  Purchase #4 $176.61   11.718%   $197.3052   $197.31   $197.30   $197.30  
  Purchase #5 $194.67   5.748%   $205.8596   $205.86   $205.85   $205.90  
  Purchase #6 $96.51   6.772%   $103.0457   $103.05   $103.05   $103.00  
  Purchase #7 $94.35   10.430%   $104.1907   $104.19   $104.20   $104.20  
  7 purchase totals = $987.11       $1,083.0206   $1,083.03   $1,083.05   $1,083.00