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 $101.40   8.861%   $110.3851   $110.39   $110.40   $110.40  
  Purchase #2 $111.91   3.438%   $115.7575   $115.76   $115.75   $115.80  
  Purchase #3 $119.65   12.580%   $134.702   $134.70   $134.70   $134.70  
  Purchase #4 $28.76   9.657%   $31.5374   $31.54   $31.55   $31.50  
  Purchase #5 $101.91   10.374%   $112.4821   $112.48   $112.50   $112.50  
  Purchase #6 $64.44   7.546%   $69.3026   $69.30   $69.30   $69.30  
  Purchase #7 $5.27   11.594%   $5.881   $5.88   $5.90   $5.90  
  7 purchase totals = $533.34       $580.0477   $580.05   $580.10   $580.10