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	$174.48	3.666%	$180.8764	$180.88	$180.90	$180.90
Purchase #2	$137.78	9.169%	$150.413	$150.41	$150.40	$150.40
Purchase #3	$25.38	8.543%	$27.5482	$27.55	$27.55	$27.50
Purchase #4	$204.62	7.338%	$219.635	$219.64	$219.65	$219.60
Purchase #5	$144.70	12.412%	$162.6602	$162.66	$162.65	$162.70
Purchase #6	$177.89	6.749%	$189.8958	$189.90	$189.90	$189.90
Purchase #7	$31.88	10.618%	$35.265	$35.27	$35.25	$35.30
7 purchase totals =	$896.73		$966.2936	$966.31	$966.30	$966.30