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 $96.91   8.141%   $104.7994   $104.80   $104.80   $104.80  
  Purchase #2 $63.76   8.468%   $69.1592   $69.16   $69.15   $69.20  
  Purchase #3 $246.82   6.213%   $262.1549   $262.15   $262.15   $262.20  
  Purchase #4 $145.71   13.169%   $164.8985   $164.90   $164.90   $164.90  
  Purchase #5 $182.35   7.502%   $196.0299   $196.03   $196.05   $196.00  
  Purchase #6 $60.48   8.332%   $65.5192   $65.52   $65.50   $65.50  
  Purchase #7 $217.94   12.502%   $245.1869   $245.19   $245.20   $245.20  
  7 purchase totals = $1,013.97       $1,107.7480   $1,107.75   $1,107.75   $1,107.80