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 $98.99   6.367%   $105.2927   $105.29   $105.30   $105.30  
  Purchase #2 $194.26   6.365%   $206.6246   $206.62   $206.60   $206.60  
  Purchase #3 $119.54   5.829%   $126.508   $126.51   $126.50   $126.50  
  Purchase #4 $127.67   5.743%   $135.0021   $135.00   $135.00   $135.00  
  Purchase #5 $152.29   3.740%   $157.9856   $157.99   $158.00   $158.00  
  Purchase #6 $245.26   6.846%   $262.0505   $262.05   $262.05   $262.10  
  Purchase #7 $198.53   6.580%   $211.5933   $211.59   $211.60   $211.60  
  7 purchase totals = $1,136.54       $1,205.0568   $1,205.05   $1,205.05   $1,205.10