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 $51.96   8.291%   $56.268   $56.27   $56.25   $56.30  
  Purchase #2 $55.73   13.148%   $63.0574   $63.06   $63.05   $63.10  
  Purchase #3 $107.84   3.581%   $111.7018   $111.70   $111.70   $111.70  
  Purchase #4 $65.30   8.544%   $70.8792   $70.88   $70.90   $70.90  
  Purchase #5 $120.26   13.614%   $136.6322   $136.63   $136.65   $136.60  
  Purchase #6 $127.50   6.403%   $135.6638   $135.66   $135.65   $135.70  
  Purchase #7 $106.54   10.501%   $117.7278   $117.73   $117.75   $117.70  
  7 purchase totals = $635.13       $691.9302   $691.93   $691.95   $692.00