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 $184.25   12.232%   $206.7875   $206.79   $206.80   $206.80  
  Purchase #2 $79.54   10.557%   $87.937   $87.94   $87.95   $87.90  
  Purchase #3 $78.94   9.698%   $86.5956   $86.60   $86.60   $86.60  
  Purchase #4 $68.63   9.361%   $75.0545   $75.05   $75.05   $75.10  
  Purchase #5 $237.80   6.221%   $252.5935   $252.59   $252.60   $252.60  
  Purchase #6 $17.39   6.203%   $18.4687   $18.47   $18.45   $18.50  
  Purchase #7 $127.52   6.782%   $136.1684   $136.17   $136.15   $136.20  
  7 purchase totals = $794.07       $863.6052   $863.61   $863.60   $863.70