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 $114.44   13.772%   $130.2007   $130.20   $130.20   $130.20  
  Purchase #2 $73.99   8.689%   $80.419   $80.42   $80.40   $80.40  
  Purchase #3 $69.88   5.180%   $73.4998   $73.50   $73.50   $73.50  
  Purchase #4 $107.63   5.592%   $113.6487   $113.65   $113.65   $113.60  
  Purchase #5 $61.52   6.790%   $65.6972   $65.70   $65.70   $65.70  
  Purchase #6 $176.98   9.251%   $193.3524   $193.35   $193.35   $193.40  
  Purchase #7 $86.45   13.794%   $98.3749   $98.37   $98.35   $98.40  
  7 purchase totals = $690.89       $755.1927   $755.19   $755.15   $755.20