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	$45.59	11.742%	$50.9432	$50.94	$50.95	$50.90
Purchase #2	$98.30	11.262%	$109.3705	$109.37	$109.35	$109.40
Purchase #3	$139.45	6.461%	$148.4599	$148.46	$148.45	$148.50
Purchase #4	$119.26	13.856%	$135.7847	$135.78	$135.80	$135.80
Purchase #5	$248.87	6.397%	$264.7902	$264.79	$264.80	$264.80
Purchase #6	$142.71	9.240%	$155.8964	$155.90	$155.90	$155.90
Purchase #7	$51.57	5.222%	$54.263	$54.26	$54.25	$54.30
7 purchase totals =	$845.75		$919.5079	$919.50	$919.50	$919.60