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	$147.36	3.497%	$152.5132	$152.51	$152.50	$152.50
Purchase #2	$129.32	10.816%	$143.3073	$143.31	$143.30	$143.30
Purchase #3	$100.61	10.289%	$110.9618	$110.96	$110.95	$111.00
Purchase #4	$215.88	7.793%	$232.7035	$232.70	$232.70	$232.70
Purchase #5	$31.25	7.113%	$33.4728	$33.47	$33.45	$33.50
Purchase #6	$52.40	10.391%	$57.8449	$57.84	$57.85	$57.80
Purchase #7	$99.54	12.177%	$111.661	$111.66	$111.65	$111.70
7 purchase totals =	$776.36		$842.4645	$842.45	$842.40	$842.50