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 $171.66   7.216%   $184.047   $184.05   $184.05   $184.00  
  Purchase #2 $108.94   12.115%   $122.1381   $122.14   $122.15   $122.10  
  Purchase #3 $145.75   11.436%   $162.418   $162.42   $162.40   $162.40  
  Purchase #4 $135.62   6.721%   $144.735   $144.74   $144.75   $144.70  
  Purchase #5 $42.46   4.330%   $44.2985   $44.30   $44.30   $44.30  
  Purchase #6 $70.97   3.592%   $73.5192   $73.52   $73.50   $73.50  
  Purchase #7 $60.47   5.649%   $63.886   $63.89   $63.90   $63.90  
  7 purchase totals = $735.87       $795.0418   $795.06   $795.05   $794.90