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 $79.51   7.723%   $85.6506   $85.65   $85.65   $85.70  
  Purchase #2 $73.87   13.231%   $83.6437   $83.64   $83.65   $83.60  
  Purchase #3 $157.43   11.534%   $175.588   $175.59   $175.60   $175.60  
  Purchase #4 $127.45   7.128%   $136.5346   $136.53   $136.55   $136.50  
  Purchase #5 $125.50   8.411%   $136.0558   $136.06   $136.05   $136.10  
  Purchase #6 $91.83   10.336%   $101.3215   $101.32   $101.30   $101.30  
  Purchase #7 $13.48   12.436%   $15.1564   $15.16   $15.15   $15.20  
  7 purchase totals = $669.07       $733.9506   $733.95   $733.95   $734.00