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	$83.98	6.854%	$89.736	$89.74	$89.75	$89.70
Purchase #2	$29.53	4.382%	$30.824	$30.82	$30.80	$30.80
Purchase #3	$84.38	6.175%	$89.5905	$89.59	$89.60	$89.60
Purchase #4	$143.36	9.122%	$156.4373	$156.44	$156.45	$156.40
Purchase #5	$46.70	4.127%	$48.6273	$48.63	$48.65	$48.60
Purchase #6	$250.64	7.677%	$269.8816	$269.88	$269.90	$269.90
Purchase #7	$210.25	11.210%	$233.819	$233.82	$233.80	$233.80
7 purchase totals =	$848.84		$918.9157	$918.92	$918.95	$918.80