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 $66.71   13.568%   $75.7612   $75.76   $75.75   $75.80  
  Purchase #2 $91.33   5.230%   $96.1066   $96.11   $96.10   $96.10  
  Purchase #3 $48.74   12.865%   $55.0104   $55.01   $55.00   $55.00  
  Purchase #4 $183.84   9.356%   $201.0401   $201.04   $201.05   $201.00  
  Purchase #5 $195.69   6.648%   $208.6995   $208.70   $208.70   $208.70  
  Purchase #6 $66.80   12.867%   $75.3952   $75.40   $75.40   $75.40  
  Purchase #7 $36.99   13.217%   $41.879   $41.88   $41.90   $41.90  
  7 purchase totals = $690.10       $753.8920   $753.90   $753.90   $753.90