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 $46.29   11.542%   $51.6328   $51.63   $51.65   $51.60  
  Purchase #2 $22.76   9.204%   $24.8548   $24.85   $24.85   $24.90  
  Purchase #3 $70.96   13.755%   $80.7205   $80.72   $80.70   $80.70  
  Purchase #4 $206.68   13.317%   $234.2036   $234.20   $234.20   $234.20  
  Purchase #5 $249.82   5.259%   $262.958   $262.96   $262.95   $263.00  
  Purchase #6 $115.70   13.267%   $131.0499   $131.05   $131.05   $131.00  
  Purchase #7 $134.97   12.387%   $151.6887   $151.69   $151.70   $151.70  
  7 purchase totals = $847.18       $937.1083   $937.10   $937.10   $937.10