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	$74.33	8.322%	$80.5157	$80.52	$80.50	$80.50
Purchase #2	$161.99	3.637%	$167.8816	$167.88	$167.90	$167.90
Purchase #3	$214.83	9.578%	$235.4064	$235.41	$235.40	$235.40
Purchase #4	$106.89	5.518%	$112.7882	$112.79	$112.80	$112.80
Purchase #5	$83.58	12.814%	$94.2899	$94.29	$94.30	$94.30
Purchase #6	$119.55	10.271%	$131.829	$131.83	$131.85	$131.80
Purchase #7	$77.88	4.686%	$81.5295	$81.53	$81.55	$81.50
7 purchase totals =	$839.05		$904.2403	$904.25	$904.30	$904.20