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 $234.78   13.768%   $267.1045   $267.10   $267.10   $267.10  
  Purchase #2 $195.56   8.752%   $212.6754   $212.68   $212.70   $212.70  
  Purchase #3 $57.48   7.202%   $61.6197   $61.62   $61.60   $61.60  
  Purchase #4 $91.65   8.805%   $99.7198   $99.72   $99.70   $99.70  
  Purchase #5 $75.68   13.736%   $86.0754   $86.08   $86.10   $86.10  
  Purchase #6 $195.69   5.215%   $205.8952   $205.90   $205.90   $205.90  
  Purchase #7 $14.36   12.554%   $16.1628   $16.16   $16.15   $16.20  
  7 purchase totals = $865.20       $949.2528   $949.26   $949.25   $949.30