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 $91.71   10.834%   $101.6459   $101.65   $101.65   $101.60  
  Purchase #2 $48.28   13.626%   $54.8586   $54.86   $54.85   $54.90  
  Purchase #3 $185.41   9.283%   $202.6216   $202.62   $202.60   $202.60  
  Purchase #4 $59.32   13.874%   $67.5501   $67.55   $67.55   $67.60  
  Purchase #5 $101.54   11.305%   $113.0191   $113.02   $113.00   $113.00  
  Purchase #6 $54.30   5.338%   $57.1985   $57.20   $57.20   $57.20  
  Purchase #7 $123.55   8.730%   $134.3359   $134.34   $134.35   $134.30  
  7 purchase totals = $664.11       $731.2297   $731.24   $731.20   $731.20