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 $60.65   6.594%   $64.6493   $64.65   $64.65   $64.60  
  Purchase #2 $57.40   12.769%   $64.7294   $64.73   $64.75   $64.70  
  Purchase #3 $165.82   5.701%   $175.2734   $175.27   $175.25   $175.30  
  Purchase #4 $37.77   11.237%   $42.0142   $42.01   $42.00   $42.00  
  Purchase #5 $222.46   7.674%   $239.5316   $239.53   $239.55   $239.50  
  Purchase #6 $195.44   8.284%   $211.6302   $211.63   $211.65   $211.60  
  Purchase #7 $22.95   5.458%   $24.2026   $24.20   $24.20   $24.20  
  7 purchase totals = $762.49       $822.0307   $822.02   $822.05   $821.90