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	$73.90	6.167%	$78.4574	$78.46	$78.45	$78.50
Purchase #2	$152.50	3.579%	$157.958	$157.96	$157.95	$158.00
Purchase #3	$169.43	3.159%	$174.7823	$174.78	$174.80	$174.80
Purchase #4	$93.98	3.841%	$97.5898	$97.59	$97.60	$97.60
Purchase #5	$243.43	6.600%	$259.4964	$259.50	$259.50	$259.50
Purchase #6	$108.49	12.263%	$121.7941	$121.79	$121.80	$121.80
Purchase #7	$99.98	12.755%	$112.7324	$112.73	$112.75	$112.70
7 purchase totals =	$941.71		$1,002.8104	$1,002.81	$1,002.85	$1,002.90