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	$122.77	6.348%	$130.5634	$130.56	$130.55	$130.60
Purchase #2	$135.70	11.184%	$150.8767	$150.88	$150.90	$150.90
Purchase #3	$88.64	7.683%	$95.4502	$95.45	$95.45	$95.50
Purchase #4	$206.56	4.445%	$215.7416	$215.74	$215.75	$215.70
Purchase #5	$154.70	10.765%	$171.3535	$171.35	$171.35	$171.40
Purchase #6	$162.83	13.519%	$184.843	$184.84	$184.85	$184.80
Purchase #7	$179.50	9.548%	$196.6387	$196.64	$196.65	$196.60
7 purchase totals =	$1,050.70		$1,145.4671	$1,145.46	$1,145.50	$1,145.50