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	$123.49	9.715%	$135.4871	$135.49	$135.50	$135.50
Purchase #2	$101.78	10.480%	$112.4465	$112.45	$112.45	$112.40
Purchase #3	$217.40	11.830%	$243.1184	$243.12	$243.10	$243.10
Purchase #4	$158.67	13.196%	$179.6081	$179.61	$179.60	$179.60
Purchase #5	$99.56	13.434%	$112.9349	$112.93	$112.95	$112.90
Purchase #6	$51.90	9.158%	$56.653	$56.65	$56.65	$56.70
Purchase #7	$250.98	10.772%	$278.0156	$278.02	$278.00	$278.00
7 purchase totals =	$1,003.78		$1,118.2636	$1,118.27	$1,118.25	$1,118.20