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 $58.35   6.155%   $61.9414   $61.94   $61.95   $61.90  
  Purchase #2 $229.49   4.153%   $239.0207   $239.02   $239.00   $239.00  
  Purchase #3 $153.58   13.653%   $174.5483   $174.55   $174.55   $174.50  
  Purchase #4 $18.69   3.233%   $19.2942   $19.29   $19.30   $19.30  
  Purchase #5 $226.46   12.666%   $255.1434   $255.14   $255.15   $255.10  
  Purchase #6 $74.81   9.106%   $81.6222   $81.62   $81.60   $81.60  
  Purchase #7 $101.28   6.563%   $107.927   $107.93   $107.95   $107.90  
  7 purchase totals = $862.66       $939.4972   $939.49   $939.50   $939.30