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 $55.86   13.358%   $63.3218   $63.32   $63.30   $63.30  
  Purchase #2 $155.56   13.219%   $176.1235   $176.12   $176.10   $176.10  
  Purchase #3 $205.80   12.526%   $231.5785   $231.58   $231.60   $231.60  
  Purchase #4 $46.61   8.495%   $50.5695   $50.57   $50.55   $50.60  
  Purchase #5 $198.49   6.555%   $211.501   $211.50   $211.50   $211.50  
  Purchase #6 $107.43   11.803%   $120.11   $120.11   $120.10   $120.10  
  Purchase #7 $152.77   6.874%   $163.2714   $163.27   $163.25   $163.30  
  7 purchase totals = $922.52       $1,016.4757   $1,016.47   $1,016.40   $1,016.50