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 $65.43   10.480%   $72.2871   $72.29   $72.30   $72.30  
  Purchase #2 $227.38   5.518%   $239.9268   $239.93   $239.95   $239.90  
  Purchase #3 $249.27   13.161%   $282.0764   $282.08   $282.10   $282.10  
  Purchase #4 $80.43   10.225%   $88.654   $88.65   $88.65   $88.70  
  Purchase #5 $17.69   8.751%   $19.2381   $19.24   $19.25   $19.20  
  Purchase #6 $109.47   10.575%   $121.0465   $121.05   $121.05   $121.00  
  Purchase #7 $52.27   12.359%   $58.73   $58.73   $58.75   $58.70  
  7 purchase totals = $801.94       $881.9589   $881.97   $882.05   $881.90