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 $61.99   12.847%   $69.9539   $69.95   $69.95   $70.00  
  Purchase #2 $165.48   3.670%   $171.5531   $171.55   $171.55   $171.60  
  Purchase #3 $174.43   6.129%   $185.1208   $185.12   $185.10   $185.10  
  Purchase #4 $184.98   6.372%   $196.7669   $196.77   $196.75   $196.80  
  Purchase #5 $8.54   12.410%   $9.5998   $9.60   $9.60   $9.60  
  Purchase #6 $159.74   6.191%   $169.6295   $169.63   $169.65   $169.60  
  Purchase #7 $118.87   9.803%   $130.5228   $130.52   $130.50   $130.50  
  7 purchase totals = $874.03       $933.1468   $933.14   $933.10   $933.20