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 $181.85   13.273%   $205.987   $205.99   $206.00   $206.00  
  Purchase #2 $9.63   7.307%   $10.3337   $10.33   $10.35   $10.30  
  Purchase #3 $138.82   5.122%   $145.9304   $145.93   $145.95   $145.90  
  Purchase #4 $134.83   8.590%   $146.4119   $146.41   $146.40   $146.40  
  Purchase #5 $138.62   9.466%   $151.7418   $151.74   $151.75   $151.70  
  Purchase #6 $57.27   13.251%   $64.8588   $64.86   $64.85   $64.90  
  Purchase #7 $216.28   6.325%   $229.9597   $229.96   $229.95   $230.00  
  7 purchase totals = $877.30       $955.2233   $955.22   $955.25   $955.20