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 $46.88   12.123%   $52.5633   $52.56   $52.55   $52.60  
  Purchase #2 $249.55   8.865%   $271.6726   $271.67   $271.65   $271.70  
  Purchase #3 $168.38   12.279%   $189.0554   $189.06   $189.05   $189.10  
  Purchase #4 $242.53   8.388%   $262.8734   $262.87   $262.85   $262.90  
  Purchase #5 $216.93   6.500%   $231.0305   $231.03   $231.05   $231.00  
  Purchase #6 $142.61   3.241%   $147.232   $147.23   $147.25   $147.20  
  Purchase #7 $240.62   5.291%   $253.3512   $253.35   $253.35   $253.40  
  7 purchase totals = $1,307.50       $1,407.7784   $1,407.77   $1,407.75   $1,407.90