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 $238.26   13.815%   $271.1756   $271.18   $271.20   $271.20  
  Purchase #2 $182.41   11.857%   $204.0384   $204.04   $204.05   $204.00  
  Purchase #3 $60.68   10.244%   $66.8961   $66.90   $66.90   $66.90  
  Purchase #4 $235.49   9.277%   $257.3364   $257.34   $257.35   $257.30  
  Purchase #5 $84.59   4.849%   $88.6918   $88.69   $88.70   $88.70  
  Purchase #6 $245.88   8.139%   $265.8922   $265.89   $265.90   $265.90  
  Purchase #7 $118.95   7.278%   $127.6072   $127.61   $127.60   $127.60  
  7 purchase totals = $1,166.26       $1,281.6377   $1,281.65   $1,281.70   $1,281.60