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 $49.49   4.781%   $51.8561   $51.86   $51.85   $51.90  
  Purchase #2 $246.81   8.380%   $267.4927   $267.49   $267.50   $267.50  
  Purchase #3 $35.95   8.623%   $39.05   $39.05   $39.05   $39.10  
  Purchase #4 $36.95   11.449%   $41.1804   $41.18   $41.20   $41.20  
  Purchase #5 $216.30   5.160%   $227.4611   $227.46   $227.45   $227.50  
  Purchase #6 $250.93   9.291%   $274.2439   $274.24   $274.25   $274.20  
  Purchase #7 $45.94   8.320%   $49.7622   $49.76   $49.75   $49.80  
  7 purchase totals = $882.37       $951.0464   $951.04   $951.05   $951.20