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 $86.94   11.545%   $96.9772   $96.98   $97.00   $97.00  
  Purchase #2 $238.57   4.610%   $249.5681   $249.57   $249.55   $249.60  
  Purchase #3 $219.77   6.148%   $233.2815   $233.28   $233.30   $233.30  
  Purchase #4 $101.86   5.770%   $107.7373   $107.74   $107.75   $107.70  
  Purchase #5 $244.81   12.610%   $275.6805   $275.68   $275.70   $275.70  
  Purchase #6 $123.94   3.177%   $127.8776   $127.88   $127.90   $127.90  
  Purchase #7 $248.70   11.552%   $277.4298   $277.43   $277.45   $277.40  
  7 purchase totals = $1,264.59       $1,368.5520   $1,368.56   $1,368.65   $1,368.60