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 $51.42   8.836%   $55.9635   $55.96   $55.95   $56.00  
  Purchase #2 $193.57   13.163%   $219.0496   $219.05   $219.05   $219.00  
  Purchase #3 $46.40   12.157%   $52.0408   $52.04   $52.05   $52.00  
  Purchase #4 $173.55   12.788%   $195.7436   $195.74   $195.75   $195.70  
  Purchase #5 $171.38   8.588%   $186.0981   $186.10   $186.10   $186.10  
  Purchase #6 $13.53   8.570%   $14.6895   $14.69   $14.70   $14.70  
  Purchase #7 $67.26   13.284%   $76.1948   $76.19   $76.20   $76.20  
  7 purchase totals = $717.11       $799.7799   $799.77   $799.80   $799.70