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 $57.57   7.629%   $61.962   $61.96   $61.95   $62.00  
  Purchase #2 $17.59   3.184%   $18.1501   $18.15   $18.15   $18.20  
  Purchase #3 $166.55   12.626%   $187.5786   $187.58   $187.60   $187.60  
  Purchase #4 $106.64   8.361%   $115.5562   $115.56   $115.55   $115.60  
  Purchase #5 $183.86   8.469%   $199.4311   $199.43   $199.45   $199.40  
  Purchase #6 $213.92   4.363%   $223.2533   $223.25   $223.25   $223.30  
  Purchase #7 $222.77   7.145%   $238.6869   $238.69   $238.70   $238.70  
  7 purchase totals = $968.90       $1,044.6182   $1,044.62   $1,044.65   $1,044.80