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	$31.36	6.211%	$33.3078	$33.31	$33.30	$33.30
Purchase #2	$94.42	5.388%	$99.5073	$99.51	$99.50	$99.50
Purchase #3	$193.76	3.609%	$200.7528	$200.75	$200.75	$200.80
Purchase #4	$149.58	3.772%	$155.2222	$155.22	$155.20	$155.20
Purchase #5	$104.73	7.349%	$112.4266	$112.43	$112.45	$112.40
Purchase #6	$88.62	6.423%	$94.3121	$94.31	$94.30	$94.30
Purchase #7	$134.41	7.810%	$144.9074	$144.91	$144.90	$144.90
7 purchase totals =	$796.88		$840.4362	$840.44	$840.40	$840.40