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 $119.72   12.373%   $134.533   $134.53   $134.55   $134.50  
  Purchase #2 $16.47   4.499%   $17.211   $17.21   $17.20   $17.20  
  Purchase #3 $146.93   9.150%   $160.3741   $160.37   $160.35   $160.40  
  Purchase #4 $94.75   8.161%   $102.4825   $102.48   $102.50   $102.50  
  Purchase #5 $28.67   3.169%   $29.5786   $29.58   $29.60   $29.60  
  Purchase #6 $240.41   5.509%   $253.6542   $253.65   $253.65   $253.70  
  Purchase #7 $244.84   5.209%   $257.5937   $257.59   $257.60   $257.60  
  7 purchase totals = $891.79       $955.4271   $955.41   $955.45   $955.50