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	$94.45	6.240%	$100.3437	$100.34	$100.35	$100.30
Purchase #2	$225.27	7.737%	$242.6991	$242.70	$242.70	$242.70
Purchase #3	$136.73	10.456%	$151.0265	$151.03	$151.05	$151.00
Purchase #4	$223.45	4.511%	$233.5298	$233.53	$233.55	$233.50
Purchase #5	$220.34	12.350%	$247.552	$247.55	$247.55	$247.60
Purchase #6	$195.61	8.324%	$211.8926	$211.89	$211.90	$211.90
Purchase #7	$81.87	10.473%	$90.4442	$90.44	$90.45	$90.40
7 purchase totals =	$1,177.72		$1,277.4879	$1,277.48	$1,277.55	$1,277.40