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 $176.94   9.271%   $193.3441   $193.34   $193.35   $193.30  
  Purchase #2 $154.83   11.452%   $172.5611   $172.56   $172.55   $172.60  
  Purchase #3 $69.86   6.828%   $74.63   $74.63   $74.65   $74.60  
  Purchase #4 $227.87   13.382%   $258.3636   $258.36   $258.35   $258.40  
  Purchase #5 $111.33   12.304%   $125.028   $125.03   $125.05   $125.00  
  Purchase #6 $153.82   8.577%   $167.0131   $167.01   $167.00   $167.00  
  Purchase #7 $69.29   5.321%   $72.9769   $72.98   $73.00   $73.00  
  7 purchase totals = $963.94       $1,063.9168   $1,063.91   $1,063.95   $1,063.90