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 $243.81   11.351%   $271.4849   $271.48   $271.50   $271.50  
  Purchase #2 $186.30   9.681%   $204.3357   $204.34   $204.35   $204.30  
  Purchase #3 $48.33   8.866%   $52.6149   $52.61   $52.60   $52.60  
  Purchase #4 $203.31   13.368%   $230.4885   $230.49   $230.50   $230.50  
  Purchase #5 $153.91   11.340%   $171.3634   $171.36   $171.35   $171.40  
  Purchase #6 $125.55   13.857%   $142.9475   $142.95   $142.95   $142.90  
  Purchase #7 $207.96   11.866%   $232.6365   $232.64   $232.65   $232.60  
  7 purchase totals = $1,169.17       $1,305.8714   $1,305.87   $1,305.90   $1,305.80