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 $183.29   6.769%   $195.6969   $195.70   $195.70   $195.70  
  Purchase #2 $92.70   9.406%   $101.4194   $101.42   $101.40   $101.40  
  Purchase #3 $73.40   9.139%   $80.108   $80.11   $80.10   $80.10  
  Purchase #4 $125.94   13.140%   $142.4885   $142.49   $142.50   $142.50  
  Purchase #5 $74.90   6.307%   $79.6239   $79.62   $79.60   $79.60  
  Purchase #6 $11.61   5.486%   $12.2469   $12.25   $12.25   $12.20  
  Purchase #7 $238.80   10.811%   $264.6167   $264.62   $264.60   $264.60  
  7 purchase totals = $800.64       $876.2003   $876.21   $876.15   $876.10