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	$243.58	9.327%	$266.2987	$266.30	$266.30	$266.30
Purchase #2	$35.71	11.476%	$39.8081	$39.81	$39.80	$39.80
Purchase #3	$103.46	12.804%	$116.707	$116.71	$116.70	$116.70
Purchase #4	$161.89	12.106%	$181.4884	$181.49	$181.50	$181.50
Purchase #5	$147.92	9.736%	$162.3215	$162.32	$162.30	$162.30
Purchase #6	$12.27	9.638%	$13.4526	$13.45	$13.45	$13.50
Purchase #7	$170.72	6.166%	$181.2466	$181.25	$181.25	$181.20
7 purchase totals =	$875.55		$961.3229	$961.33	$961.30	$961.30