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	$78.91	13.457%	$89.5289	$89.53	$89.55	$89.50
Purchase #2	$176.29	11.619%	$196.7731	$196.77	$196.75	$196.80
Purchase #3	$185.25	11.400%	$206.3685	$206.37	$206.35	$206.40
Purchase #4	$57.65	4.768%	$60.3988	$60.40	$60.40	$60.40
Purchase #5	$247.92	12.500%	$278.91	$278.91	$278.90	$278.90
Purchase #6	$248.65	6.546%	$264.9266	$264.93	$264.95	$264.90
Purchase #7	$72.46	5.516%	$76.4569	$76.46	$76.45	$76.50
7 purchase totals =	$1,067.13		$1,173.3628	$1,173.37	$1,173.35	$1,173.40