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 $40.27   11.209%   $44.7839   $44.78   $44.80   $44.80  
  Purchase #2 $222.35   5.235%   $233.99   $233.99   $234.00   $234.00  
  Purchase #3 $143.39   8.171%   $155.1064   $155.11   $155.10   $155.10  
  Purchase #4 $129.83   11.176%   $144.3398   $144.34   $144.35   $144.30  
  Purchase #5 $24.62   9.151%   $26.873   $26.87   $26.85   $26.90  
  Purchase #6 $229.32   13.362%   $259.9617   $259.96   $259.95   $260.00  
  Purchase #7 $246.38   3.362%   $254.6633   $254.66   $254.65   $254.70  
  7 purchase totals = $1,036.16       $1,119.7181   $1,119.71   $1,119.70   $1,119.80