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 $185.44   13.594%   $210.6487   $210.65   $210.65   $210.60  
  Purchase #2 $147.85   12.375%   $166.1464   $166.15   $166.15   $166.10  
  Purchase #3 $84.98   11.309%   $94.5904   $94.59   $94.60   $94.60  
  Purchase #4 $92.74   4.429%   $96.8475   $96.85   $96.85   $96.80  
  Purchase #5 $163.33   5.262%   $171.9244   $171.92   $171.90   $171.90  
  Purchase #6 $24.74   6.455%   $26.337   $26.34   $26.35   $26.30  
  Purchase #7 $195.69   11.385%   $217.9693   $217.97   $217.95   $218.00  
  7 purchase totals = $894.77       $984.4637   $984.47   $984.45   $984.30