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 $86.64   13.688%   $98.4993   $98.50   $98.50   $98.50  
  Purchase #2 $250.69   9.510%   $274.5306   $274.53   $274.55   $274.50  
  Purchase #3 $161.96   6.326%   $172.2056   $172.21   $172.20   $172.20  
  Purchase #4 $140.67   3.300%   $145.3121   $145.31   $145.30   $145.30  
  Purchase #5 $233.60   3.854%   $242.6029   $242.60   $242.60   $242.60  
  Purchase #6 $225.58   8.800%   $245.431   $245.43   $245.45   $245.40  
  Purchase #7 $155.41   13.445%   $176.3049   $176.30   $176.30   $176.30  
  7 purchase totals = $1,254.55       $1,354.8864   $1,354.88   $1,354.90   $1,354.80