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 $211.85   6.804%   $226.2643   $226.26   $226.25   $226.30  
  Purchase #2 $100.83   13.783%   $114.7274   $114.73   $114.75   $114.70  
  Purchase #3 $24.70   9.225%   $26.9786   $26.98   $27.00   $27.00  
  Purchase #4 $160.94   3.359%   $166.346   $166.35   $166.35   $166.30  
  Purchase #5 $238.42   5.342%   $251.1564   $251.16   $251.15   $251.20  
  Purchase #6 $161.51   12.634%   $181.9152   $181.92   $181.90   $181.90  
  Purchase #7 $188.32   4.591%   $196.9658   $196.97   $196.95   $197.00  
  7 purchase totals = $1,086.57       $1,164.3537   $1,164.37   $1,164.35   $1,164.40