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 $63.92   12.258%   $71.7553   $71.76   $71.75   $71.80  
  Purchase #2 $148.94   12.500%   $167.5575   $167.56   $167.55   $167.60  
  Purchase #3 $221.67   9.760%   $243.305   $243.31   $243.30   $243.30  
  Purchase #4 $32.48   12.747%   $36.6202   $36.62   $36.60   $36.60  
  Purchase #5 $15.76   4.633%   $16.4902   $16.49   $16.50   $16.50  
  Purchase #6 $242.93   4.276%   $253.3177   $253.32   $253.30   $253.30  
  Purchase #7 $156.54   4.563%   $163.6829   $163.68   $163.70   $163.70  
  7 purchase totals = $882.24       $952.7288   $952.74   $952.70   $952.80