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	$85.75	7.289%	$92.0003	$92.00	$92.00	$92.00
Purchase #2	$250.84	8.172%	$271.3386	$271.34	$271.35	$271.30
Purchase #3	$141.70	12.774%	$159.8008	$159.80	$159.80	$159.80
Purchase #4	$84.77	10.152%	$93.3759	$93.38	$93.40	$93.40
Purchase #5	$168.37	12.813%	$189.9432	$189.94	$189.95	$189.90
Purchase #6	$66.46	9.712%	$72.9146	$72.91	$72.90	$72.90
Purchase #7	$113.40	12.451%	$127.5194	$127.52	$127.50	$127.50
7 purchase totals =	$911.29		$1,006.8928	$1,006.89	$1,006.90	$1,006.80