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 $217.68   12.790%   $245.5213   $245.52   $245.50   $245.50  
  Purchase #2 $108.60   7.129%   $116.3421   $116.34   $116.35   $116.30  
  Purchase #3 $56.33   9.790%   $61.8447   $61.84   $61.85   $61.80  
  Purchase #4 $193.30   5.708%   $204.3336   $204.33   $204.35   $204.30  
  Purchase #5 $242.41   8.672%   $263.4318   $263.43   $263.45   $263.40  
  Purchase #6 $110.91   5.290%   $116.7771   $116.78   $116.80   $116.80  
  Purchase #7 $247.58   8.497%   $268.6169   $268.62   $268.60   $268.60  
  7 purchase totals = $1,176.81       $1,276.8675   $1,276.86   $1,276.90   $1,276.70