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 $21.78   10.259%   $24.0144   $24.01   $24.00   $24.00  
  Purchase #2 $247.39   8.269%   $267.8467   $267.85   $267.85   $267.80  
  Purchase #3 $211.82   13.721%   $240.8838   $240.88   $240.90   $240.90  
  Purchase #4 $174.61   10.553%   $193.0366   $193.04   $193.05   $193.00  
  Purchase #5 $117.96   3.657%   $122.2738   $122.27   $122.25   $122.30  
  Purchase #6 $150.29   11.783%   $167.9987   $168.00   $168.00   $168.00  
  Purchase #7 $248.81   4.480%   $259.9567   $259.96   $259.95   $260.00  
  7 purchase totals = $1,172.66       $1,276.0107   $1,276.01   $1,276.00   $1,276.00