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 $55.68   12.114%   $62.4251   $62.43   $62.45   $62.40  
  Purchase #2 $12.43   9.617%   $13.6254   $13.63   $13.65   $13.60  
  Purchase #3 $95.84   8.292%   $103.7871   $103.79   $103.80   $103.80  
  Purchase #4 $176.96   10.246%   $195.0913   $195.09   $195.10   $195.10  
  Purchase #5 $34.67   6.437%   $36.9017   $36.90   $36.90   $36.90  
  Purchase #6 $238.79   3.322%   $246.7226   $246.72   $246.70   $246.70  
  Purchase #7 $222.28   11.149%   $247.062   $247.06   $247.05   $247.10  
  7 purchase totals = $836.65       $905.6152   $905.62   $905.65   $905.60