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 $24.45   8.371%   $26.4967   $26.50   $26.50   $26.50  
  Purchase #2 $208.74   9.610%   $228.7999   $228.80   $228.80   $228.80  
  Purchase #3 $76.53   10.724%   $84.7371   $84.74   $84.75   $84.70  
  Purchase #4 $103.48   4.271%   $107.8996   $107.90   $107.90   $107.90  
  Purchase #5 $132.98   11.773%   $148.6357   $148.64   $148.65   $148.60  
  Purchase #6 $244.71   9.169%   $267.1475   $267.15   $267.15   $267.10  
  Purchase #7 $96.89   10.256%   $106.827   $106.83   $106.85   $106.80  
  7 purchase totals = $887.78       $970.5435   $970.56   $970.60   $970.40