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	$58.47	12.803%	$65.9559	$65.96	$65.95	$66.00
Purchase #2	$243.89	12.154%	$273.5324	$273.53	$273.55	$273.50
Purchase #3	$90.93	12.753%	$102.5263	$102.53	$102.55	$102.50
Purchase #4	$156.35	8.359%	$169.4193	$169.42	$169.40	$169.40
Purchase #5	$171.88	11.123%	$190.9982	$191.00	$191.00	$191.00
Purchase #6	$242.67	6.658%	$258.827	$258.83	$258.85	$258.80
Purchase #7	$145.72	3.662%	$151.0563	$151.06	$151.05	$151.10
7 purchase totals =	$1,109.91		$1,212.3154	$1,212.33	$1,212.35	$1,212.30