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 $168.25   8.347%   $182.2938   $182.29   $182.30   $182.30  
  Purchase #2 $86.98   7.639%   $93.6244   $93.62   $93.60   $93.60  
  Purchase #3 $62.48   12.714%   $70.4237   $70.42   $70.40   $70.40  
  Purchase #4 $203.43   9.260%   $222.2676   $222.27   $222.25   $222.30  
  Purchase #5 $199.74   9.519%   $218.7533   $218.75   $218.75   $218.80  
  Purchase #6 $121.80   12.212%   $136.6742   $136.67   $136.65   $136.70  
  Purchase #7 $110.62   9.602%   $121.2417   $121.24   $121.25   $121.20  
  7 purchase totals = $953.30       $1,045.2787   $1,045.26   $1,045.20   $1,045.30