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 $46.57   8.109%   $50.3464   $50.35   $50.35   $50.30  
  Purchase #2 $224.39   9.383%   $245.4445   $245.44   $245.45   $245.40  
  Purchase #3 $212.86   9.830%   $233.7841   $233.78   $233.80   $233.80  
  Purchase #4 $199.44   6.250%   $211.905   $211.91   $211.90   $211.90  
  Purchase #5 $53.78   7.531%   $57.8302   $57.83   $57.85   $57.80  
  Purchase #6 $32.75   11.435%   $36.495   $36.50   $36.50   $36.50  
  Purchase #7 $29.28   4.317%   $30.544   $30.54   $30.55   $30.50  
  7 purchase totals = $799.07       $866.3492   $866.35   $866.40   $866.20