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 $79.38   12.459%   $89.27   $89.27   $89.25   $89.30  
  Purchase #2 $40.82   6.164%   $43.3361   $43.34   $43.35   $43.30  
  Purchase #3 $82.42   12.808%   $92.9764   $92.98   $93.00   $93.00  
  Purchase #4 $227.49   13.278%   $257.6961   $257.70   $257.70   $257.70  
  Purchase #5 $185.94   4.620%   $194.5304   $194.53   $194.55   $194.50  
  Purchase #6 $87.87   8.244%   $95.114   $95.11   $95.10   $95.10  
  Purchase #7 $156.31   12.379%   $175.6596   $175.66   $175.65   $175.70  
  7 purchase totals = $860.23       $948.5826   $948.59   $948.60   $948.60