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 $95.57   6.657%   $101.9321   $101.93   $101.95   $101.90  
  Purchase #2 $250.54   6.377%   $266.5169   $266.52   $266.50   $266.50  
  Purchase #3 $73.74   13.536%   $83.7214   $83.72   $83.70   $83.70  
  Purchase #4 $234.51   10.664%   $259.5181   $259.52   $259.50   $259.50  
  Purchase #5 $51.87   6.806%   $55.4003   $55.40   $55.40   $55.40  
  Purchase #6 $230.49   7.236%   $247.1683   $247.17   $247.15   $247.20  
  Purchase #7 $233.42   3.120%   $240.7027   $240.70   $240.70   $240.70  
  7 purchase totals = $1,170.14       $1,254.9598   $1,254.96   $1,254.90   $1,254.90