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	$98.70	5.494%	$104.1226	$104.12	$104.10	$104.10
Purchase #2	$18.66	7.485%	$20.0567	$20.06	$20.05	$20.10
Purchase #3	$77.79	5.526%	$82.0887	$82.09	$82.10	$82.10
Purchase #4	$40.53	9.340%	$44.3155	$44.32	$44.30	$44.30
Purchase #5	$113.38	13.293%	$128.4516	$128.45	$128.45	$128.50
Purchase #6	$58.36	5.653%	$61.6591	$61.66	$61.65	$61.70
Purchase #7	$67.91	6.622%	$72.407	$72.41	$72.40	$72.40
7 purchase totals =	$475.33		$513.1012	$513.11	$513.05	$513.20