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 $61.72   12.778%   $69.6066   $69.61   $69.60   $69.60  
  Purchase #2 $41.37   8.632%   $44.9411   $44.94   $44.95   $44.90  
  Purchase #3 $209.75   6.250%   $222.8594   $222.86   $222.85   $222.90  
  Purchase #4 $166.65   3.866%   $173.0927   $173.09   $173.10   $173.10  
  Purchase #5 $60.54   4.210%   $63.0887   $63.09   $63.10   $63.10  
  Purchase #6 $167.89   11.180%   $186.6601   $186.66   $186.65   $186.70  
  Purchase #7 $134.40   6.415%   $143.0218   $143.02   $143.00   $143.00  
  7 purchase totals = $842.32       $903.2704   $903.27   $903.25   $903.30