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	$40.52	12.361%	$45.5287	$45.53	$45.55	$45.50
Purchase #2	$169.31	10.775%	$187.5532	$187.55	$187.55	$187.60
Purchase #3	$180.85	5.412%	$190.6376	$190.64	$190.65	$190.60
Purchase #4	$59.41	8.623%	$64.5329	$64.53	$64.55	$64.50
Purchase #5	$221.71	4.551%	$231.8	$231.80	$231.80	$231.80
Purchase #6	$213.50	7.199%	$228.8699	$228.87	$228.85	$228.90
Purchase #7	$127.36	11.288%	$141.7364	$141.74	$141.75	$141.70
7 purchase totals =	$1,012.66		$1,090.6587	$1,090.66	$1,090.70	$1,090.60