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 $222.57   8.287%   $241.0144   $241.01   $241.00   $241.00  
  Purchase #2 $218.85   3.696%   $226.9387   $226.94   $226.95   $226.90  
  Purchase #3 $147.48   4.235%   $153.7258   $153.73   $153.75   $153.70  
  Purchase #4 $15.43   3.554%   $15.9784   $15.98   $16.00   $16.00  
  Purchase #5 $234.75   9.769%   $257.6827   $257.68   $257.70   $257.70  
  Purchase #6 $75.65   5.128%   $79.5293   $79.53   $79.55   $79.50  
  Purchase #7 $17.39   10.310%   $19.1829   $19.18   $19.20   $19.20  
  7 purchase totals = $932.12       $994.0522   $994.05   $994.15   $994.00