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 $230.53   13.589%   $261.8567   $261.86   $261.85   $261.90  
  Purchase #2 $177.93   7.471%   $191.2232   $191.22   $191.20   $191.20  
  Purchase #3 $239.31   5.459%   $252.3739   $252.37   $252.35   $252.40  
  Purchase #4 $67.66   5.490%   $71.3745   $71.37   $71.35   $71.40  
  Purchase #5 $5.68   5.184%   $5.9745   $5.97   $5.95   $6.00  
  Purchase #6 $245.49   13.237%   $277.9855   $277.99   $278.00   $278.00  
  Purchase #7 $147.44   10.322%   $162.6588   $162.66   $162.65   $162.70  
  7 purchase totals = $1,114.04       $1,223.4471   $1,223.44   $1,223.35   $1,223.60