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	$159.29	6.815%	$170.1456	$170.15	$170.15	$170.10
Purchase #2	$100.49	5.705%	$106.223	$106.22	$106.20	$106.20
Purchase #3	$199.96	9.231%	$218.4183	$218.42	$218.40	$218.40
Purchase #4	$35.71	4.794%	$37.4219	$37.42	$37.40	$37.40
Purchase #5	$152.70	6.319%	$162.3491	$162.35	$162.35	$162.30
Purchase #6	$135.62	13.218%	$153.5463	$153.55	$153.55	$153.50
Purchase #7	$142.51	8.657%	$154.8471	$154.85	$154.85	$154.80
7 purchase totals =	$926.28		$1,002.9513	$1,002.96	$1,002.90	$1,002.70