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 $32.74   6.363%   $34.8232   $34.82   $34.80   $34.80  
  Purchase #2 $224.31   9.326%   $245.2292   $245.23   $245.25   $245.20  
  Purchase #3 $6.71   10.652%   $7.4247   $7.42   $7.40   $7.40  
  Purchase #4 $104.39   12.646%   $117.5912   $117.59   $117.60   $117.60  
  Purchase #5 $195.66   7.577%   $210.4852   $210.49   $210.50   $210.50  
  Purchase #6 $165.49   12.799%   $186.6711   $186.67   $186.65   $186.70  
  Purchase #7 $209.95   11.620%   $234.3462   $234.35   $234.35   $234.30  
  7 purchase totals = $939.25       $1,036.5708   $1,036.57   $1,036.55   $1,036.50