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 $125.82   13.421%   $142.7063   $142.71   $142.70   $142.70  
  Purchase #2 $243.86   12.506%   $274.3571   $274.36   $274.35   $274.40  
  Purchase #3 $48.84   3.199%   $50.4024   $50.40   $50.40   $50.40  
  Purchase #4 $234.47   6.594%   $249.931   $249.93   $249.95   $249.90  
  Purchase #5 $99.33   6.411%   $105.698   $105.70   $105.70   $105.70  
  Purchase #6 $14.65   3.491%   $15.1614   $15.16   $15.15   $15.20  
  Purchase #7 $78.73   3.210%   $81.2572   $81.26   $81.25   $81.30  
  7 purchase totals = $845.70       $919.5134   $919.52   $919.50   $919.60