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	$30.34	11.693%	$33.8877	$33.89	$33.90	$33.90
Purchase #2	$115.56	7.466%	$124.1877	$124.19	$124.20	$124.20
Purchase #3	$209.31	6.818%	$223.5808	$223.58	$223.60	$223.60
Purchase #4	$24.69	3.153%	$25.4685	$25.47	$25.45	$25.50
Purchase #5	$64.26	12.458%	$72.2655	$72.27	$72.25	$72.30
Purchase #6	$50.70	8.317%	$54.9167	$54.92	$54.90	$54.90
Purchase #7	$149.52	6.572%	$159.3465	$159.35	$159.35	$159.30
7 purchase totals =	$644.38		$693.6534	$693.67	$693.65	$693.70