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 $106.86   12.273%   $119.9749   $119.97   $119.95   $120.00  
  Purchase #2 $86.72   6.731%   $92.5571   $92.56   $92.55   $92.60  
  Purchase #3 $138.80   9.474%   $151.9499   $151.95   $151.95   $151.90  
  Purchase #4 $56.74   7.252%   $60.8548   $60.85   $60.85   $60.90  
  Purchase #5 $233.81   12.499%   $263.0339   $263.03   $263.05   $263.00  
  Purchase #6 $192.64   11.519%   $214.8302   $214.83   $214.85   $214.80  
  Purchase #7 $152.68   10.277%   $168.3709   $168.37   $168.35   $168.40  
  7 purchase totals = $968.25       $1,071.5717   $1,071.56   $1,071.55   $1,071.60