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	$229.72	9.411%	$251.3389	$251.34	$251.35	$251.30
Purchase #2	$217.84	4.817%	$228.3334	$228.33	$228.35	$228.30
Purchase #3	$138.98	9.745%	$152.5236	$152.52	$152.50	$152.50
Purchase #4	$61.91	8.279%	$67.0355	$67.04	$67.05	$67.00
Purchase #5	$119.76	11.429%	$133.4474	$133.45	$133.45	$133.40
Purchase #6	$67.57	11.672%	$75.4568	$75.46	$75.45	$75.50
Purchase #7	$149.28	4.713%	$156.3156	$156.32	$156.30	$156.30
7 purchase totals =	$985.06		$1,064.4512	$1,064.46	$1,064.45	$1,064.30