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	$203.30	4.718%	$212.8917	$212.89	$212.90	$212.90
Purchase #2	$102.73	9.314%	$112.2983	$112.30	$112.30	$112.30
Purchase #3	$169.89	5.787%	$179.7215	$179.72	$179.70	$179.70
Purchase #4	$112.86	12.331%	$126.7768	$126.78	$126.80	$126.80
Purchase #5	$247.69	9.537%	$271.3122	$271.31	$271.30	$271.30
Purchase #6	$118.27	10.720%	$130.9485	$130.95	$130.95	$130.90
Purchase #7	$182.37	3.790%	$189.2818	$189.28	$189.30	$189.30
7 purchase totals =	$1,137.11		$1,223.2308	$1,223.23	$1,223.25	$1,223.20