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 $206.39   13.867%   $235.0101   $235.01   $235.00   $235.00  
  Purchase #2 $21.58   6.719%   $23.03   $23.03   $23.05   $23.00  
  Purchase #3 $152.76   4.428%   $159.5242   $159.52   $159.50   $159.50  
  Purchase #4 $223.55   13.706%   $254.1898   $254.19   $254.20   $254.20  
  Purchase #5 $119.81   11.782%   $133.926   $133.93   $133.95   $133.90  
  Purchase #6 $79.55   6.675%   $84.86   $84.86   $84.85   $84.90  
  Purchase #7 $109.56   6.774%   $116.9816   $116.98   $117.00   $117.00  
  7 purchase totals = $913.20       $1,007.5217   $1,007.52   $1,007.55   $1,007.50