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 $234.75   4.638%   $245.6377   $245.64   $245.65   $245.60  
  Purchase #2 $173.96   11.116%   $193.2974   $193.30   $193.30   $193.30  
  Purchase #3 $231.62   5.492%   $244.3406   $244.34   $244.35   $244.30  
  Purchase #4 $90.37   6.402%   $96.1555   $96.16   $96.15   $96.20  
  Purchase #5 $184.26   4.487%   $192.5277   $192.53   $192.55   $192.50  
  Purchase #6 $235.84   13.684%   $268.1123   $268.11   $268.10   $268.10  
  Purchase #7 $226.40   5.804%   $239.5403   $239.54   $239.55   $239.50  
  7 purchase totals = $1,377.20       $1,479.6115   $1,479.62   $1,479.65   $1,479.50