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 $59.58   7.395%   $63.9859   $63.99   $64.00   $64.00  
  Purchase #2 $248.71   8.256%   $269.2435   $269.24   $269.25   $269.20  
  Purchase #3 $180.84   8.441%   $196.1047   $196.10   $196.10   $196.10  
  Purchase #4 $156.61   8.835%   $170.4465   $170.45   $170.45   $170.40  
  Purchase #5 $76.48   6.349%   $81.3357   $81.34   $81.35   $81.30  
  Purchase #6 $127.30   6.185%   $135.1735   $135.17   $135.15   $135.20  
  Purchase #7 $93.50   7.258%   $100.2862   $100.29   $100.30   $100.30  
  7 purchase totals = $943.02       $1,016.5760   $1,016.58   $1,016.60   $1,016.50