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	$165.47	11.433%	$184.3882	$184.39	$184.40	$184.40
Purchase #2	$205.44	9.688%	$225.343	$225.34	$225.35	$225.30
Purchase #3	$89.80	11.221%	$99.8765	$99.88	$99.90	$99.90
Purchase #4	$82.84	3.404%	$85.6599	$85.66	$85.65	$85.70
Purchase #5	$239.93	4.243%	$250.1102	$250.11	$250.10	$250.10
Purchase #6	$70.26	10.192%	$77.4209	$77.42	$77.40	$77.40
Purchase #7	$10.96	13.125%	$12.3985	$12.40	$12.40	$12.40
7 purchase totals =	$864.70		$935.1972	$935.20	$935.20	$935.20