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 $85.50   10.152%   $94.18   $94.18   $94.20   $94.20  
  Purchase #2 $78.48   3.244%   $81.0259   $81.03   $81.05   $81.00  
  Purchase #3 $118.69   6.579%   $126.4986   $126.50   $126.50   $126.50  
  Purchase #4 $206.90   12.158%   $232.0549   $232.05   $232.05   $232.10  
  Purchase #5 $117.44   8.796%   $127.77   $127.77   $127.75   $127.80  
  Purchase #6 $206.25   11.419%   $229.8017   $229.80   $229.80   $229.80  
  Purchase #7 $13.44   10.682%   $14.8757   $14.88   $14.90   $14.90  
  7 purchase totals = $826.70       $906.2068   $906.21   $906.25   $906.30