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	$186.55	7.497%	$200.5357	$200.54	$200.55	$200.50
Purchase #2	$97.59	12.193%	$109.4891	$109.49	$109.50	$109.50
Purchase #3	$59.46	3.839%	$61.7427	$61.74	$61.75	$61.70
Purchase #4	$19.44	6.159%	$20.6373	$20.64	$20.65	$20.60
Purchase #5	$39.50	5.693%	$41.7487	$41.75	$41.75	$41.70
Purchase #6	$138.71	8.314%	$150.2423	$150.24	$150.25	$150.20
Purchase #7	$240.84	12.704%	$271.4363	$271.44	$271.45	$271.40
7 purchase totals =	$782.09		$855.8321	$855.84	$855.90	$855.60