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 $201.79   4.658%   $211.1894   $211.19   $211.20   $211.20  
  Purchase #2 $25.66   12.345%   $28.8277   $28.83   $28.85   $28.80  
  Purchase #3 $58.99   13.294%   $66.8321   $66.83   $66.85   $66.80  
  Purchase #4 $96.48   6.517%   $102.7676   $102.77   $102.75   $102.80  
  Purchase #5 $235.73   7.671%   $253.8128   $253.81   $253.80   $253.80  
  Purchase #6 $15.27   3.551%   $15.8122   $15.81   $15.80   $15.80  
  Purchase #7 $137.35   3.439%   $142.0735   $142.07   $142.05   $142.10  
  7 purchase totals = $771.27       $821.3153   $821.31   $821.30   $821.30