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 $60.31   5.823%   $63.8219   $63.82   $63.80   $63.80  
  Purchase #2 $58.54   11.293%   $65.1509   $65.15   $65.15   $65.20  
  Purchase #3 $174.60   3.492%   $180.697   $180.70   $180.70   $180.70  
  Purchase #4 $52.25   9.737%   $57.3376   $57.34   $57.35   $57.30  
  Purchase #5 $56.58   13.537%   $64.2392   $64.24   $64.25   $64.20  
  Purchase #6 $50.33   12.478%   $56.6102   $56.61   $56.60   $56.60  
  Purchase #7 $218.50   9.267%   $238.7484   $238.75   $238.75   $238.70  
  7 purchase totals = $671.11       $726.6052   $726.61   $726.60   $726.50