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	$49.95	10.148%	$55.0189	$55.02	$55.00	$55.00
Purchase #2	$191.45	13.220%	$216.7597	$216.76	$216.75	$216.80
Purchase #3	$159.25	12.666%	$179.4206	$179.42	$179.40	$179.40
Purchase #4	$204.51	3.623%	$211.9194	$211.92	$211.90	$211.90
Purchase #5	$55.73	6.404%	$59.2989	$59.30	$59.30	$59.30
Purchase #6	$78.46	5.445%	$82.7321	$82.73	$82.75	$82.70
Purchase #7	$51.68	13.304%	$58.5555	$58.56	$58.55	$58.60
7 purchase totals =	$791.03		$863.7051	$863.71	$863.65	$863.70