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	$41.84	3.592%	$43.3429	$43.34	$43.35	$43.30
Purchase #2	$102.39	8.502%	$111.0952	$111.10	$111.10	$111.10
Purchase #3	$129.60	9.819%	$142.3254	$142.33	$142.35	$142.30
Purchase #4	$179.58	5.606%	$189.6473	$189.65	$189.65	$189.60
Purchase #5	$34.86	9.765%	$38.2641	$38.26	$38.25	$38.30
Purchase #6	$89.98	8.412%	$97.5491	$97.55	$97.55	$97.50
Purchase #7	$63.71	9.702%	$69.8911	$69.89	$69.90	$69.90
7 purchase totals =	$641.96		$692.1151	$692.12	$692.15	$692.00