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 $173.99   5.424%   $183.4272   $183.43   $183.45   $183.40  
  Purchase #2 $81.70   11.795%   $91.3365   $91.34   $91.35   $91.30  
  Purchase #3 $247.91   5.556%   $261.6839   $261.68   $261.70   $261.70  
  Purchase #4 $86.26   11.211%   $95.9306   $95.93   $95.95   $95.90  
  Purchase #5 $189.98   6.167%   $201.6961   $201.70   $201.70   $201.70  
  Purchase #6 $59.99   5.263%   $63.1473   $63.15   $63.15   $63.10  
  Purchase #7 $148.74   11.786%   $166.2705   $166.27   $166.25   $166.30  
  7 purchase totals = $988.57       $1,063.4921   $1,063.50   $1,063.55   $1,063.40