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 $233.31   6.432%   $248.3165   $248.32   $248.30   $248.30  
  Purchase #2 $62.64   9.482%   $68.5795   $68.58   $68.60   $68.60  
  Purchase #3 $67.88   13.190%   $76.8334   $76.83   $76.85   $76.80  
  Purchase #4 $181.49   13.754%   $206.4521   $206.45   $206.45   $206.50  
  Purchase #5 $27.62   5.263%   $29.0736   $29.07   $29.05   $29.10  
  Purchase #6 $184.48   7.454%   $198.2311   $198.23   $198.25   $198.20  
  Purchase #7 $156.97   6.427%   $167.0585   $167.06   $167.05   $167.10  
  7 purchase totals = $914.39       $994.5447   $994.54   $994.55   $994.60