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 $40.41   10.629%   $44.7052   $44.71   $44.70   $44.70  
  Purchase #2 $93.37   3.412%   $96.5558   $96.56   $96.55   $96.60  
  Purchase #3 $78.98   4.676%   $82.6731   $82.67   $82.65   $82.70  
  Purchase #4 $127.69   12.607%   $143.7879   $143.79   $143.80   $143.80  
  Purchase #5 $30.88   3.318%   $31.9046   $31.90   $31.90   $31.90  
  Purchase #6 $51.52   11.496%   $57.4427   $57.44   $57.45   $57.40  
  Purchase #7 $159.80   5.117%   $167.977   $167.98   $168.00   $168.00  
  7 purchase totals = $582.65       $625.0463   $625.05   $625.05   $625.10