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	$233.48	4.153%	$243.1764	$243.18	$243.20	$243.20
Purchase #2	$193.68	12.320%	$217.5414	$217.54	$217.55	$217.50
Purchase #3	$226.26	4.308%	$236.0073	$236.01	$236.00	$236.00
Purchase #4	$96.26	4.524%	$100.6148	$100.61	$100.60	$100.60
Purchase #5	$73.35	12.580%	$82.5774	$82.58	$82.60	$82.60
Purchase #6	$6.58	7.238%	$7.0563	$7.06	$7.05	$7.10
Purchase #7	$104.76	10.758%	$116.0301	$116.03	$116.05	$116.00
7 purchase totals =	$934.37		$1,003.0037	$1,003.01	$1,003.05	$1,003.00