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 $158.55   10.174%   $174.6809   $174.68   $174.70   $174.70  
  Purchase #2 $237.47   4.393%   $247.9021   $247.90   $247.90   $247.90  
  Purchase #3 $123.66   4.735%   $129.5153   $129.52   $129.50   $129.50  
  Purchase #4 $190.70   10.624%   $210.96   $210.96   $210.95   $211.00  
  Purchase #5 $142.50   10.684%   $157.7247   $157.72   $157.70   $157.70  
  Purchase #6 $237.94   12.429%   $267.5136   $267.51   $267.50   $267.50  
  Purchase #7 $224.61   10.643%   $248.5152   $248.52   $248.50   $248.50  
  7 purchase totals = $1,315.43       $1,436.8118   $1,436.81   $1,436.75   $1,436.80