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 $86.42   13.534%   $98.1161   $98.12   $98.10   $98.10  
  Purchase #2 $232.87   6.704%   $248.4816   $248.48   $248.50   $248.50  
  Purchase #3 $105.77   6.770%   $112.9306   $112.93   $112.95   $112.90  
  Purchase #4 $247.31   9.449%   $270.6783   $270.68   $270.70   $270.70  
  Purchase #5 $141.46   4.560%   $147.9106   $147.91   $147.90   $147.90  
  Purchase #6 $67.27   10.344%   $74.2284   $74.23   $74.25   $74.20  
  Purchase #7 $194.73   9.496%   $213.2216   $213.22   $213.20   $213.20  
  7 purchase totals = $1,075.83       $1,165.5672   $1,165.57   $1,165.60   $1,165.50