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 $60.40   11.150%   $67.1346   $67.13   $67.15   $67.10  
  Purchase #2 $212.61   6.687%   $226.8272   $226.83   $226.85   $226.80  
  Purchase #3 $39.26   8.150%   $42.4597   $42.46   $42.45   $42.50  
  Purchase #4 $24.90   3.458%   $25.761   $25.76   $25.75   $25.80  
  Purchase #5 $42.72   4.675%   $44.7172   $44.72   $44.70   $44.70  
  Purchase #6 $209.63   6.430%   $223.1092   $223.11   $223.10   $223.10  
  Purchase #7 $205.77   5.845%   $217.7973   $217.80   $217.80   $217.80  
  7 purchase totals = $795.29       $847.8062   $847.81   $847.80   $847.80