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	$38.33	9.827%	$42.0967	$42.10	$42.10	$42.10
Purchase #2	$190.94	6.261%	$202.8948	$202.89	$202.90	$202.90
Purchase #3	$59.42	5.580%	$62.7356	$62.74	$62.75	$62.70
Purchase #4	$189.43	11.168%	$210.5855	$210.59	$210.60	$210.60
Purchase #5	$102.85	6.241%	$109.2689	$109.27	$109.25	$109.30
Purchase #6	$89.94	9.780%	$98.7361	$98.74	$98.75	$98.70
Purchase #7	$189.41	9.410%	$207.2335	$207.23	$207.25	$207.20
7 purchase totals =	$860.32		$933.5511	$933.56	$933.60	$933.50