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 $114.98   6.302%   $122.226   $122.23   $122.25   $122.20  
  Purchase #2 $187.37   9.217%   $204.6399   $204.64   $204.65   $204.60  
  Purchase #3 $52.54   11.402%   $58.5306   $58.53   $58.55   $58.50  
  Purchase #4 $115.84   3.652%   $120.0705   $120.07   $120.05   $120.10  
  Purchase #5 $7.89   12.653%   $8.8883   $8.89   $8.90   $8.90  
  Purchase #6 $221.50   4.730%   $231.977   $231.98   $232.00   $232.00  
  Purchase #7 $24.39   12.250%   $27.3778   $27.38   $27.40   $27.40  
  7 purchase totals = $724.51       $773.7101   $773.72   $773.80   $773.70