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	$240.29	12.498%	$270.3214	$270.32	$270.30	$270.30
Purchase #2	$178.83	5.379%	$188.4493	$188.45	$188.45	$188.40
Purchase #3	$196.39	11.826%	$219.6151	$219.62	$219.60	$219.60
Purchase #4	$90.97	11.142%	$101.1059	$101.11	$101.10	$101.10
Purchase #5	$52.94	4.873%	$55.5198	$55.52	$55.50	$55.50
Purchase #6	$84.76	6.137%	$89.9617	$89.96	$89.95	$90.00
Purchase #7	$237.62	11.417%	$264.7491	$264.75	$264.75	$264.70
7 purchase totals =	$1,081.80		$1,189.7223	$1,189.73	$1,189.65	$1,189.60