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 $59.45   7.576%   $63.9539   $63.95   $63.95   $64.00  
  Purchase #2 $77.41   3.150%   $79.8484   $79.85   $79.85   $79.80  
  Purchase #3 $78.53   12.544%   $88.3808   $88.38   $88.40   $88.40  
  Purchase #4 $222.31   8.475%   $241.1508   $241.15   $241.15   $241.20  
  Purchase #5 $174.61   12.324%   $196.1289   $196.13   $196.15   $196.10  
  Purchase #6 $18.94   8.135%   $20.4808   $20.48   $20.50   $20.50  
  Purchase #7 $87.99   5.714%   $93.0177   $93.02   $93.00   $93.00  
  7 purchase totals = $719.24       $782.9613   $782.96   $783.00   $783.00