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 $200.32   7.821%   $215.987   $215.99   $216.00   $216.00  
  Purchase #2 $187.45   5.820%   $198.3596   $198.36   $198.35   $198.40  
  Purchase #3 $126.95   9.800%   $139.3911   $139.39   $139.40   $139.40  
  Purchase #4 $186.34   9.576%   $204.1839   $204.18   $204.20   $204.20  
  Purchase #5 $168.91   5.715%   $178.5632   $178.56   $178.55   $178.60  
  Purchase #6 $69.63   8.626%   $75.6363   $75.64   $75.65   $75.60  
  Purchase #7 $54.74   3.821%   $56.8316   $56.83   $56.85   $56.80  
  7 purchase totals = $994.34       $1,068.9527   $1,068.95   $1,069.00   $1,069.00