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 $91.86   5.535%   $96.9445   $96.94   $96.95   $96.90  
  Purchase #2 $154.76   11.749%   $172.9428   $172.94   $172.95   $172.90  
  Purchase #3 $218.29   10.299%   $240.7717   $240.77   $240.75   $240.80  
  Purchase #4 $28.67   5.591%   $30.2729   $30.27   $30.25   $30.30  
  Purchase #5 $187.29   13.791%   $213.1192   $213.12   $213.10   $213.10  
  Purchase #6 $198.66   12.835%   $224.158   $224.16   $224.15   $224.20  
  Purchase #7 $162.74   13.712%   $185.0549   $185.05   $185.05   $185.10  
  7 purchase totals = $1,042.27       $1,163.2640   $1,163.25   $1,163.20   $1,163.30