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 $61.83   6.754%   $66.006   $66.01   $66.00   $66.00  
  Purchase #2 $149.44   8.559%   $162.2306   $162.23   $162.25   $162.20  
  Purchase #3 $117.63   13.590%   $133.6159   $133.62   $133.60   $133.60  
  Purchase #4 $202.64   3.330%   $209.3879   $209.39   $209.40   $209.40  
  Purchase #5 $82.36   13.868%   $93.7817   $93.78   $93.80   $93.80  
  Purchase #6 $128.71   3.641%   $133.3963   $133.40   $133.40   $133.40  
  Purchase #7 $24.87   9.263%   $27.1737   $27.17   $27.15   $27.20  
  7 purchase totals = $767.48       $825.5921   $825.60   $825.60   $825.60