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 $64.51   13.647%   $73.3137   $73.31   $73.30   $73.30  
  Purchase #2 $114.28   8.518%   $124.0144   $124.01   $124.00   $124.00  
  Purchase #3 $151.64   10.724%   $167.9019   $167.90   $167.90   $167.90  
  Purchase #4 $196.54   3.711%   $203.8336   $203.83   $203.85   $203.80  
  Purchase #5 $233.58   7.209%   $250.4188   $250.42   $250.40   $250.40  
  Purchase #6 $71.62   5.608%   $75.6364   $75.64   $75.65   $75.60  
  Purchase #7 $161.95   8.149%   $175.1473   $175.15   $175.15   $175.10  
  7 purchase totals = $994.12       $1,070.2661   $1,070.26   $1,070.25   $1,070.10