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 $50.68   6.434%   $53.9408   $53.94   $53.95   $53.90  
  Purchase #2 $66.81   5.466%   $70.4618   $70.46   $70.45   $70.50  
  Purchase #3 $56.38   6.353%   $59.9618   $59.96   $59.95   $60.00  
  Purchase #4 $126.46   6.190%   $134.2879   $134.29   $134.30   $134.30  
  Purchase #5 $177.43   13.697%   $201.7326   $201.73   $201.75   $201.70  
  Purchase #6 $90.41   9.539%   $99.0342   $99.03   $99.05   $99.00  
  Purchase #7 $49.87   11.272%   $55.4913   $55.49   $55.50   $55.50  
  7 purchase totals = $618.04       $674.9104   $674.90   $674.95   $674.90