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 $224.55   10.713%   $248.606   $248.61   $248.60   $248.60  
  Purchase #2 $44.35   7.315%   $47.5942   $47.59   $47.60   $47.60  
  Purchase #3 $79.79   10.474%   $88.1472   $88.15   $88.15   $88.10  
  Purchase #4 $233.66   6.303%   $248.3876   $248.39   $248.40   $248.40  
  Purchase #5 $203.92   13.151%   $230.7375   $230.74   $230.75   $230.70  
  Purchase #6 $72.28   3.695%   $74.9507   $74.95   $74.95   $75.00  
  Purchase #7 $250.62   4.580%   $262.0984   $262.10   $262.10   $262.10  
  7 purchase totals = $1,109.17       $1,200.5216   $1,200.53   $1,200.55   $1,200.50