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 $46.30   11.213%   $51.4916   $51.49   $51.50   $51.50  
  Purchase #2 $248.43   9.271%   $271.4619   $271.46   $271.45   $271.50  
  Purchase #3 $211.51   7.138%   $226.6076   $226.61   $226.60   $226.60  
  Purchase #4 $204.92   9.135%   $223.6394   $223.64   $223.65   $223.60  
  Purchase #5 $77.64   4.414%   $81.067   $81.07   $81.05   $81.10  
  Purchase #6 $209.39   5.770%   $221.4718   $221.47   $221.45   $221.50  
  Purchase #7 $174.52   13.341%   $197.8027   $197.80   $197.80   $197.80  
  7 purchase totals = $1,172.71       $1,273.5420   $1,273.54   $1,273.50   $1,273.60