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 $63.70   7.232%   $68.3068   $68.31   $68.30   $68.30  
  Purchase #2 $150.83   8.161%   $163.1392   $163.14   $163.15   $163.10  
  Purchase #3 $41.77   11.649%   $46.6358   $46.64   $46.65   $46.60  
  Purchase #4 $93.76   10.326%   $103.4417   $103.44   $103.45   $103.40  
  Purchase #5 $84.79   13.467%   $96.2087   $96.21   $96.20   $96.20  
  Purchase #6 $175.90   12.112%   $197.205   $197.21   $197.20   $197.20  
  Purchase #7 $101.98   9.678%   $111.8496   $111.85   $111.85   $111.80  
  7 purchase totals = $712.73       $786.7868   $786.80   $786.80   $786.60