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 $24.47   6.433%   $26.0442   $26.04   $26.05   $26.00  
  Purchase #2 $238.25   4.349%   $248.6115   $248.61   $248.60   $248.60  
  Purchase #3 $197.66   13.655%   $224.6505   $224.65   $224.65   $224.70  
  Purchase #4 $114.75   6.126%   $121.7796   $121.78   $121.80   $121.80  
  Purchase #5 $214.47   5.199%   $225.6203   $225.62   $225.60   $225.60  
  Purchase #6 $59.82   13.712%   $68.0225   $68.02   $68.00   $68.00  
  Purchase #7 $70.96   11.838%   $79.3602   $79.36   $79.35   $79.40  
  7 purchase totals = $920.38       $994.0888   $994.08   $994.05   $994.10