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 $92.95   6.717%   $99.1935   $99.19   $99.20   $99.20  
  Purchase #2 $227.99   3.356%   $235.6413   $235.64   $235.65   $235.60  
  Purchase #3 $148.88   7.646%   $160.2634   $160.26   $160.25   $160.30  
  Purchase #4 $117.51   13.752%   $133.67   $133.67   $133.65   $133.70  
  Purchase #5 $93.84   8.151%   $101.4889   $101.49   $101.50   $101.50  
  Purchase #6 $103.83   13.359%   $117.7006   $117.70   $117.70   $117.70  
  Purchase #7 $139.31   5.329%   $146.7338   $146.73   $146.75   $146.70  
  7 purchase totals = $924.31       $994.6915   $994.68   $994.70   $994.70