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 $76.51   3.194%   $78.9537   $78.95   $78.95   $79.00  
  Purchase #2 $119.27   5.527%   $125.8621   $125.86   $125.85   $125.90  
  Purchase #3 $115.51   10.494%   $127.6316   $127.63   $127.65   $127.60  
  Purchase #4 $59.74   6.589%   $63.6763   $63.68   $63.70   $63.70  
  Purchase #5 $219.61   9.604%   $240.7013   $240.70   $240.70   $240.70  
  Purchase #6 $219.75   5.287%   $231.3682   $231.37   $231.35   $231.40  
  Purchase #7 $40.64   7.404%   $43.649   $43.65   $43.65   $43.60  
  7 purchase totals = $851.03       $911.8422   $911.84   $911.85   $911.90