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 $193.60   10.147%   $213.2446   $213.24   $213.25   $213.20  
  Purchase #2 $96.85   13.226%   $109.6594   $109.66   $109.65   $109.70  
  Purchase #3 $26.95   12.714%   $30.3764   $30.38   $30.40   $30.40  
  Purchase #4 $100.81   11.831%   $112.7368   $112.74   $112.75   $112.70  
  Purchase #5 $88.79   6.659%   $94.7025   $94.70   $94.70   $94.70  
  Purchase #6 $151.62   12.623%   $170.759   $170.76   $170.75   $170.80  
  Purchase #7 $207.97   5.581%   $219.5768   $219.58   $219.60   $219.60  
  7 purchase totals = $866.59       $951.0555   $951.06   $951.10   $951.10