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 $68.31   3.534%   $70.7241   $70.72   $70.70   $70.70  
  Purchase #2 $227.73   10.179%   $250.9106   $250.91   $250.90   $250.90  
  Purchase #3 $206.38   7.421%   $221.6955   $221.70   $221.70   $221.70  
  Purchase #4 $73.53   3.178%   $75.8668   $75.87   $75.85   $75.90  
  Purchase #5 $163.93   4.695%   $171.6265   $171.63   $171.65   $171.60  
  Purchase #6 $237.47   5.284%   $250.0179   $250.02   $250.00   $250.00  
  Purchase #7 $26.61   6.343%   $28.2979   $28.30   $28.30   $28.30  
  7 purchase totals = $1,003.96       $1,069.1393   $1,069.15   $1,069.10   $1,069.10