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 $58.68   3.483%   $60.7238   $60.72   $60.70   $60.70  
  Purchase #2 $58.57   5.103%   $61.5588   $61.56   $61.55   $61.60  
  Purchase #3 $13.72   11.671%   $15.3213   $15.32   $15.30   $15.30  
  Purchase #4 $185.58   8.772%   $201.8591   $201.86   $201.85   $201.90  
  Purchase #5 $89.54   6.228%   $95.1166   $95.12   $95.10   $95.10  
  Purchase #6 $233.59   13.766%   $265.746   $265.75   $265.75   $265.70  
  Purchase #7 $72.66   6.858%   $77.643   $77.64   $77.65   $77.60  
  7 purchase totals = $712.34       $777.9686   $777.97   $777.90   $777.90