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 $208.82   7.672%   $224.8407   $224.84   $224.85   $224.80  
  Purchase #2 $5.94   6.617%   $6.333   $6.33   $6.35   $6.30  
  Purchase #3 $55.88   10.837%   $61.9357   $61.94   $61.95   $61.90  
  Purchase #4 $167.93   8.726%   $182.5836   $182.58   $182.60   $182.60  
  Purchase #5 $68.86   11.300%   $76.6412   $76.64   $76.65   $76.60  
  Purchase #6 $93.97   12.862%   $106.0564   $106.06   $106.05   $106.10  
  Purchase #7 $106.30   11.426%   $118.4458   $118.45   $118.45   $118.40  
  7 purchase totals = $707.70       $776.8364   $776.84   $776.90   $776.70