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 $79.48   11.874%   $88.9175   $88.92   $88.90   $88.90  
  Purchase #2 $209.68   3.479%   $216.9748   $216.97   $216.95   $217.00  
  Purchase #3 $22.88   3.203%   $23.6128   $23.61   $23.60   $23.60  
  Purchase #4 $149.25   9.732%   $163.775   $163.78   $163.80   $163.80  
  Purchase #5 $238.62   8.593%   $259.1246   $259.12   $259.10   $259.10  
  Purchase #6 $50.27   10.480%   $55.5383   $55.54   $55.55   $55.50  
  Purchase #7 $57.25   12.202%   $64.2356   $64.24   $64.25   $64.20  
  7 purchase totals = $807.43       $872.1786   $872.18   $872.15   $872.10