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 $106.61   11.661%   $119.0418   $119.04   $119.05   $119.00  
  Purchase #2 $121.70   13.303%   $137.8898   $137.89   $137.90   $137.90  
  Purchase #3 $207.63   7.684%   $223.5843   $223.58   $223.60   $223.60  
  Purchase #4 $179.91   5.407%   $189.6377   $189.64   $189.65   $189.60  
  Purchase #5 $61.60   4.437%   $64.3332   $64.33   $64.35   $64.30  
  Purchase #6 $115.41   3.416%   $119.3524   $119.35   $119.35   $119.40  
  Purchase #7 $131.81   11.679%   $147.2041   $147.20   $147.20   $147.20  
  7 purchase totals = $924.67       $1,001.0433   $1,001.03   $1,001.10   $1,001.00