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 $132.41   11.762%   $147.9841   $147.98   $148.00   $148.00  
  Purchase #2 $127.83   6.114%   $135.6455   $135.65   $135.65   $135.60  
  Purchase #3 $52.54   3.440%   $54.3474   $54.35   $54.35   $54.30  
  Purchase #4 $167.80   4.394%   $175.1731   $175.17   $175.15   $175.20  
  Purchase #5 $143.78   3.351%   $148.5981   $148.60   $148.60   $148.60  
  Purchase #6 $248.71   5.679%   $262.8342   $262.83   $262.85   $262.80  
  Purchase #7 $156.95   10.784%   $173.8755   $173.88   $173.90   $173.90  
  7 purchase totals = $1,030.02       $1,098.4579   $1,098.46   $1,098.50   $1,098.40