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 $32.85   11.371%   $36.5854   $36.59   $36.60   $36.60  
  Purchase #2 $135.97   13.526%   $154.3613   $154.36   $154.35   $154.40  
  Purchase #3 $162.61   9.591%   $178.2059   $178.21   $178.20   $178.20  
  Purchase #4 $196.51   6.781%   $209.8353   $209.84   $209.85   $209.80  
  Purchase #5 $99.85   3.306%   $103.151   $103.15   $103.15   $103.20  
  Purchase #6 $160.36   13.151%   $181.4489   $181.45   $181.45   $181.40  
  Purchase #7 $233.64   8.587%   $253.7027   $253.70   $253.70   $253.70  
  7 purchase totals = $1,021.79       $1,117.2905   $1,117.30   $1,117.30   $1,117.30