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 $228.65   6.202%   $242.8309   $242.83   $242.85   $242.80  
  Purchase #2 $94.64   3.166%   $97.6363   $97.64   $97.65   $97.60  
  Purchase #3 $157.96   10.215%   $174.0956   $174.10   $174.10   $174.10  
  Purchase #4 $179.63   13.363%   $203.634   $203.63   $203.65   $203.60  
  Purchase #5 $119.33   12.564%   $134.3226   $134.32   $134.30   $134.30  
  Purchase #6 $68.36   11.572%   $76.2706   $76.27   $76.25   $76.30  
  Purchase #7 $182.96   13.473%   $207.6102   $207.61   $207.60   $207.60  
  7 purchase totals = $1,031.53       $1,136.4002   $1,136.40   $1,136.40   $1,136.30