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	$38.41	12.452%	$43.1928	$43.19	$43.20	$43.20
Purchase #2	$19.94	8.470%	$21.6289	$21.63	$21.65	$21.60
Purchase #3	$243.56	12.730%	$274.5652	$274.57	$274.55	$274.60
Purchase #4	$220.28	8.106%	$238.1359	$238.14	$238.15	$238.10
Purchase #5	$240.69	9.494%	$263.5411	$263.54	$263.55	$263.50
Purchase #6	$94.59	11.182%	$105.1671	$105.17	$105.15	$105.20
Purchase #7	$61.50	9.794%	$67.5233	$67.52	$67.50	$67.50
7 purchase totals =	$918.97		$1,013.7543	$1,013.76	$1,013.75	$1,013.70