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 $213.76   12.277%   $240.0033   $240.00   $240.00   $240.00  
  Purchase #2 $119.55   6.149%   $126.9011   $126.90   $126.90   $126.90  
  Purchase #3 $85.64   11.316%   $95.331   $95.33   $95.35   $95.30  
  Purchase #4 $39.58   10.585%   $43.7695   $43.77   $43.75   $43.80  
  Purchase #5 $187.27   13.619%   $212.7743   $212.77   $212.75   $212.80  
  Purchase #6 $175.85   5.328%   $185.2193   $185.22   $185.20   $185.20  
  Purchase #7 $242.36   10.633%   $268.1301   $268.13   $268.15   $268.10  
  7 purchase totals = $1,064.01       $1,172.1286   $1,172.12   $1,172.10   $1,172.10