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	$241.87	11.411%	$269.4698	$269.47	$269.45	$269.50
Purchase #2	$249.33	5.485%	$263.0058	$263.01	$263.00	$263.00
Purchase #3	$133.76	12.187%	$150.0613	$150.06	$150.05	$150.10
Purchase #4	$156.42	12.138%	$175.4063	$175.41	$175.40	$175.40
Purchase #5	$210.43	7.628%	$226.4816	$226.48	$226.50	$226.50
Purchase #6	$157.25	9.474%	$172.1479	$172.15	$172.15	$172.10
Purchase #7	$85.30	5.171%	$89.7109	$89.71	$89.70	$89.70
7 purchase totals =	$1,234.36		$1,346.2836	$1,346.29	$1,346.25	$1,346.30