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 $88.59   13.212%   $100.2945   $100.29   $100.30   $100.30  
  Purchase #2 $186.58   6.582%   $198.8607   $198.86   $198.85   $198.90  
  Purchase #3 $58.76   3.269%   $60.6809   $60.68   $60.70   $60.70  
  Purchase #4 $196.30   4.623%   $205.3749   $205.37   $205.35   $205.40  
  Purchase #5 $15.90   3.587%   $16.4703   $16.47   $16.45   $16.50  
  Purchase #6 $111.66   6.198%   $118.5807   $118.58   $118.60   $118.60  
  Purchase #7 $95.30   8.624%   $103.5187   $103.52   $103.50   $103.50  
  7 purchase totals = $753.09       $803.7807   $803.77   $803.75   $803.90