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 $241.25   10.809%   $267.3267   $267.33   $267.35   $267.30  
  Purchase #2 $48.33   5.642%   $51.0568   $51.06   $51.05   $51.10  
  Purchase #3 $72.40   7.680%   $77.9603   $77.96   $77.95   $78.00  
  Purchase #4 $112.80   3.612%   $116.8743   $116.87   $116.85   $116.90  
  Purchase #5 $239.70   6.254%   $254.6908   $254.69   $254.70   $254.70  
  Purchase #6 $214.26   4.771%   $224.4823   $224.48   $224.50   $224.50  
  Purchase #7 $28.37   6.390%   $30.1828   $30.18   $30.20   $30.20  
  7 purchase totals = $957.11       $1,022.5740   $1,022.57   $1,022.60   $1,022.70