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 $226.82   7.405%   $243.616   $243.62   $243.60   $243.60  
  Purchase #2 $34.38   6.431%   $36.591   $36.59   $36.60   $36.60  
  Purchase #3 $69.88   11.588%   $77.9777   $77.98   $78.00   $78.00  
  Purchase #4 $204.92   9.425%   $224.2337   $224.23   $224.25   $224.20  
  Purchase #5 $237.49   12.324%   $266.7583   $266.76   $266.75   $266.80  
  Purchase #6 $177.86   4.795%   $186.3884   $186.39   $186.40   $186.40  
  Purchase #7 $211.99   3.597%   $219.6153   $219.62   $219.60   $219.60  
  7 purchase totals = $1,163.34       $1,255.1804   $1,255.19   $1,255.20   $1,255.20