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	$74.28	5.334%	$78.2421	$78.24	$78.25	$78.20
Purchase #2	$186.46	3.438%	$192.8705	$192.87	$192.85	$192.90
Purchase #3	$85.90	4.643%	$89.8883	$89.89	$89.90	$89.90
Purchase #4	$199.51	12.289%	$224.0278	$224.03	$224.05	$224.00
Purchase #5	$34.97	4.124%	$36.4122	$36.41	$36.40	$36.40
Purchase #6	$109.40	6.103%	$116.0767	$116.08	$116.10	$116.10
Purchase #7	$175.83	7.668%	$189.3126	$189.31	$189.30	$189.30
7 purchase totals =	$866.35		$926.8302	$926.83	$926.85	$926.80