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 $67.66   6.264%   $71.8982   $71.90   $71.90   $71.90  
  Purchase #2 $173.36   11.363%   $193.0589   $193.06   $193.05   $193.10  
  Purchase #3 $97.62   9.539%   $106.932   $106.93   $106.95   $106.90  
  Purchase #4 $137.63   3.364%   $142.2599   $142.26   $142.25   $142.30  
  Purchase #5 $209.77   8.218%   $227.0089   $227.01   $227.00   $227.00  
  Purchase #6 $114.55   13.553%   $130.075   $130.08   $130.10   $130.10  
  Purchase #7 $165.79   6.715%   $176.9228   $176.92   $176.90   $176.90  
  7 purchase totals = $966.38       $1,048.1557   $1,048.16   $1,048.15   $1,048.20