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	$92.44	11.153%	$102.7498	$102.75	$102.75	$102.70
Purchase #2	$109.95	3.606%	$113.9148	$113.91	$113.90	$113.90
Purchase #3	$246.40	9.396%	$269.5517	$269.55	$269.55	$269.60
Purchase #4	$188.45	6.536%	$200.7671	$200.77	$200.75	$200.80
Purchase #5	$223.65	12.152%	$250.8279	$250.83	$250.85	$250.80
Purchase #6	$185.60	6.134%	$196.9847	$196.98	$197.00	$197.00
Purchase #7	$53.78	3.639%	$55.7371	$55.74	$55.75	$55.70
7 purchase totals =	$1,100.27		$1,190.5331	$1,190.53	$1,190.55	$1,190.50