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 $58.84   11.411%   $65.5542   $65.55   $65.55   $65.60  
  Purchase #2 $170.82   12.556%   $192.2682   $192.27   $192.25   $192.30  
  Purchase #3 $182.41   12.432%   $205.0872   $205.09   $205.10   $205.10  
  Purchase #4 $51.69   7.437%   $55.5342   $55.53   $55.55   $55.50  
  Purchase #5 $43.65   5.467%   $46.0363   $46.04   $46.05   $46.00  
  Purchase #6 $241.51   6.360%   $256.87   $256.87   $256.85   $256.90  
  Purchase #7 $110.71   10.244%   $122.0511   $122.05   $122.05   $122.10  
  7 purchase totals = $859.63       $943.4012   $943.40   $943.40   $943.50