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	$31.53	12.328%	$35.417	$35.42	$35.40	$35.40
Purchase #2	$47.74	5.702%	$50.4621	$50.46	$50.45	$50.50
Purchase #3	$5.94	9.777%	$6.5208	$6.52	$6.50	$6.50
Purchase #4	$105.50	12.280%	$118.4554	$118.46	$118.45	$118.50
Purchase #5	$131.44	3.746%	$136.3637	$136.36	$136.35	$136.40
Purchase #6	$46.42	13.211%	$52.5525	$52.55	$52.55	$52.60
Purchase #7	$81.39	13.608%	$92.4656	$92.47	$92.45	$92.50
7 purchase totals =	$449.96		$492.2371	$492.24	$492.15	$492.40