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 $239.75   3.682%   $248.5776   $248.58   $248.60   $248.60  
  Purchase #2 $167.58   11.581%   $186.9874   $186.99   $187.00   $187.00  
  Purchase #3 $246.43   9.440%   $269.693   $269.69   $269.70   $269.70  
  Purchase #4 $175.79   6.282%   $186.8331   $186.83   $186.85   $186.80  
  Purchase #5 $177.91   11.704%   $198.7326   $198.73   $198.75   $198.70  
  Purchase #6 $139.92   6.644%   $149.2163   $149.22   $149.20   $149.20  
  Purchase #7 $80.36   7.432%   $86.3324   $86.33   $86.35   $86.30  
  7 purchase totals = $1,227.74       $1,326.3724   $1,326.37   $1,326.45   $1,326.30