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 $229.27   7.502%   $246.4698   $246.47   $246.45   $246.50  
  Purchase #2 $90.27   12.232%   $101.3118   $101.31   $101.30   $101.30  
  Purchase #3 $233.33   9.271%   $254.962   $254.96   $254.95   $255.00  
  Purchase #4 $34.61   4.780%   $36.2644   $36.26   $36.25   $36.30  
  Purchase #5 $148.95   13.451%   $168.9853   $168.99   $169.00   $169.00  
  Purchase #6 $46.41   13.686%   $52.7617   $52.76   $52.75   $52.80  
  Purchase #7 $186.39   13.466%   $211.4893   $211.49   $211.50   $211.50  
  7 purchase totals = $969.23       $1,072.2443   $1,072.24   $1,072.20   $1,072.40