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 $231.83   9.803%   $254.5563   $254.56   $254.55   $254.60  
  Purchase #2 $241.35   11.808%   $269.8486   $269.85   $269.85   $269.80  
  Purchase #3 $40.76   7.864%   $43.9654   $43.97   $43.95   $44.00  
  Purchase #4 $175.33   10.210%   $193.2312   $193.23   $193.25   $193.20  
  Purchase #5 $147.43   12.664%   $166.1005   $166.10   $166.10   $166.10  
  Purchase #6 $52.57   5.321%   $55.3672   $55.37   $55.35   $55.40  
  Purchase #7 $241.90   11.337%   $269.3242   $269.32   $269.30   $269.30  
  7 purchase totals = $1,131.17       $1,252.3934   $1,252.40   $1,252.35   $1,252.40