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	$247.89	10.140%	$273.026	$273.03	$273.05	$273.00
Purchase #2	$176.57	8.512%	$191.5996	$191.60	$191.60	$191.60
Purchase #3	$84.85	5.320%	$89.364	$89.36	$89.35	$89.40
Purchase #4	$104.34	7.821%	$112.5004	$112.50	$112.50	$112.50
Purchase #5	$203.83	12.498%	$229.3047	$229.30	$229.30	$229.30
Purchase #6	$187.58	3.589%	$194.3122	$194.31	$194.30	$194.30
Purchase #7	$58.91	12.519%	$66.2849	$66.28	$66.30	$66.30
7 purchase totals =	$1,063.97		$1,156.3918	$1,156.38	$1,156.40	$1,156.40