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 $106.52   11.440%   $118.7059   $118.71   $118.70   $118.70  
  Purchase #2 $173.66   12.226%   $194.8917   $194.89   $194.90   $194.90  
  Purchase #3 $130.33   8.193%   $141.0079   $141.01   $141.00   $141.00  
  Purchase #4 $37.25   12.848%   $42.0359   $42.04   $42.05   $42.00  
  Purchase #5 $88.47   5.651%   $93.4694   $93.47   $93.45   $93.50  
  Purchase #6 $130.29   8.706%   $141.633   $141.63   $141.65   $141.60  
  Purchase #7 $206.37   9.387%   $225.742   $225.74   $225.75   $225.70  
  7 purchase totals = $872.89       $957.4858   $957.49   $957.50   $957.40