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 $203.46   6.330%   $216.339   $216.34   $216.35   $216.30  
  Purchase #2 $86.54   8.462%   $93.863   $93.86   $93.85   $93.90  
  Purchase #3 $32.73   3.811%   $33.9773   $33.98   $34.00   $34.00  
  Purchase #4 $192.91   3.664%   $199.9782   $199.98   $200.00   $200.00  
  Purchase #5 $115.25   10.403%   $127.2395   $127.24   $127.25   $127.20  
  Purchase #6 $210.63   5.248%   $221.6839   $221.68   $221.70   $221.70  
  Purchase #7 $243.34   3.650%   $252.2219   $252.22   $252.20   $252.20  
  7 purchase totals = $1,084.86       $1,145.3028   $1,145.30   $1,145.35   $1,145.30