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	$55.89	13.306%	$63.3267	$63.33	$63.35	$63.30
Purchase #2	$67.50	4.322%	$70.4174	$70.42	$70.40	$70.40
Purchase #3	$215.39	12.418%	$242.1371	$242.14	$242.15	$242.10
Purchase #4	$69.45	13.572%	$78.8758	$78.88	$78.90	$78.90
Purchase #5	$207.86	11.765%	$232.3147	$232.31	$232.30	$232.30
Purchase #6	$54.82	7.708%	$59.0455	$59.05	$59.05	$59.00
Purchase #7	$41.70	10.745%	$46.1807	$46.18	$46.20	$46.20
7 purchase totals =	$712.61		$792.2979	$792.31	$792.35	$792.20