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 $109.67   11.626%   $122.4202   $122.42   $122.40   $122.40  
  Purchase #2 $22.97   7.183%   $24.6199   $24.62   $24.60   $24.60  
  Purchase #3 $43.88   12.492%   $49.3615   $49.36   $49.35   $49.40  
  Purchase #4 $161.72   8.869%   $176.0629   $176.06   $176.05   $176.10  
  Purchase #5 $244.88   4.258%   $255.307   $255.31   $255.30   $255.30  
  Purchase #6 $225.70   8.839%   $245.6496   $245.65   $245.65   $245.60  
  Purchase #7 $146.47   4.481%   $153.0333   $153.03   $153.05   $153.00  
  7 purchase totals = $955.29       $1,026.4544   $1,026.45   $1,026.40   $1,026.40