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 $203.78   6.147%   $216.3064   $216.31   $216.30   $216.30  
  Purchase #2 $190.87   6.837%   $203.9198   $203.92   $203.90   $203.90  
  Purchase #3 $84.98   11.864%   $95.062   $95.06   $95.05   $95.10  
  Purchase #4 $61.65   10.361%   $68.0376   $68.04   $68.05   $68.00  
  Purchase #5 $11.27   9.183%   $12.3049   $12.30   $12.30   $12.30  
  Purchase #6 $129.30   5.779%   $136.7722   $136.77   $136.75   $136.80  
  Purchase #7 $194.97   4.438%   $203.6228   $203.62   $203.60   $203.60  
  7 purchase totals = $876.82       $936.0257   $936.02   $935.95   $936.00