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 $46.40   12.363%   $52.1364   $52.14   $52.15   $52.10  
  Purchase #2 $178.86   3.631%   $185.3544   $185.35   $185.35   $185.40  
  Purchase #3 $197.38   11.564%   $220.205   $220.21   $220.20   $220.20  
  Purchase #4 $30.85   11.775%   $34.4826   $34.48   $34.50   $34.50  
  Purchase #5 $22.59   10.408%   $24.9412   $24.94   $24.95   $24.90  
  Purchase #6 $242.98   13.160%   $274.9562   $274.96   $274.95   $275.00  
  Purchase #7 $138.68   7.119%   $148.5526   $148.55   $148.55   $148.60  
  7 purchase totals = $857.74       $940.6284   $940.63   $940.65   $940.70