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 $244.86   7.406%   $262.9943   $262.99   $263.00   $263.00  
  Purchase #2 $179.48   4.560%   $187.6643   $187.66   $187.65   $187.70  
  Purchase #3 $87.54   11.462%   $97.5738   $97.57   $97.55   $97.60  
  Purchase #4 $240.84   10.262%   $265.555   $265.56   $265.55   $265.60  
  Purchase #5 $175.43   5.445%   $184.9822   $184.98   $185.00   $185.00  
  Purchase #6 $185.48   10.163%   $204.3303   $204.33   $204.35   $204.30  
  Purchase #7 $241.43   13.602%   $274.2693   $274.27   $274.25   $274.30  
  7 purchase totals = $1,355.06       $1,477.3692   $1,477.36   $1,477.35   $1,477.50