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 $196.77   4.710%   $206.0379   $206.04   $206.05   $206.00  
  Purchase #2 $164.53   5.164%   $173.0263   $173.03   $173.05   $173.00  
  Purchase #3 $11.47   4.310%   $11.9644   $11.96   $11.95   $12.00  
  Purchase #4 $246.98   4.306%   $257.615   $257.62   $257.60   $257.60  
  Purchase #5 $163.26   11.395%   $181.8635   $181.86   $181.85   $181.90  
  Purchase #6 $202.35   10.748%   $224.0986   $224.10   $224.10   $224.10  
  Purchase #7 $157.88   11.156%   $175.4931   $175.49   $175.50   $175.50  
  7 purchase totals = $1,143.24       $1,230.0988   $1,230.10   $1,230.10   $1,230.10