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	$72.46	12.539%	$81.5458	$81.55	$81.55	$81.50
Purchase #2	$175.26	8.591%	$190.3166	$190.32	$190.30	$190.30
Purchase #3	$150.78	9.858%	$165.6439	$165.64	$165.65	$165.60
Purchase #4	$188.62	13.283%	$213.6744	$213.67	$213.65	$213.70
Purchase #5	$145.67	13.595%	$165.4738	$165.47	$165.45	$165.50
Purchase #6	$152.75	7.691%	$164.498	$164.50	$164.50	$164.50
Purchase #7	$94.89	8.263%	$102.7308	$102.73	$102.75	$102.70
7 purchase totals =	$980.43		$1,083.8833	$1,083.88	$1,083.85	$1,083.80