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 $65.86   13.169%   $74.5331   $74.53   $74.55   $74.50  
  Purchase #2 $23.25   7.655%   $25.0298   $25.03   $25.05   $25.00  
  Purchase #3 $230.60   8.632%   $250.5054   $250.51   $250.50   $250.50  
  Purchase #4 $214.91   9.208%   $234.6989   $234.70   $234.70   $234.70  
  Purchase #5 $63.54   4.416%   $66.3459   $66.35   $66.35   $66.30  
  Purchase #6 $88.57   11.121%   $98.4199   $98.42   $98.40   $98.40  
  Purchase #7 $197.87   7.613%   $212.9338   $212.93   $212.95   $212.90  
  7 purchase totals = $884.60       $962.4668   $962.47   $962.50   $962.30