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 $52.69   6.760%   $56.2518   $56.25   $56.25   $56.30  
  Purchase #2 $29.97   13.418%   $33.9914   $33.99   $34.00   $34.00  
  Purchase #3 $114.77   5.609%   $121.2074   $121.21   $121.20   $121.20  
  Purchase #4 $182.42   6.260%   $193.8395   $193.84   $193.85   $193.80  
  Purchase #5 $95.78   10.846%   $106.1683   $106.17   $106.15   $106.20  
  Purchase #6 $133.65   13.537%   $151.7422   $151.74   $151.75   $151.70  
  Purchase #7 $56.48   7.205%   $60.5494   $60.55   $60.55   $60.50  
  7 purchase totals = $665.76       $723.7500   $723.75   $723.75   $723.70