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	$198.64	12.697%	$223.8613	$223.86	$223.85	$223.90
Purchase #2	$26.58	5.743%	$28.1065	$28.11	$28.10	$28.10
Purchase #3	$191.99	12.792%	$216.5494	$216.55	$216.55	$216.50
Purchase #4	$184.44	4.152%	$192.0979	$192.10	$192.10	$192.10
Purchase #5	$148.50	3.859%	$154.2306	$154.23	$154.25	$154.20
Purchase #6	$82.55	10.156%	$90.9338	$90.93	$90.95	$90.90
Purchase #7	$90.37	3.214%	$93.2745	$93.27	$93.25	$93.30
7 purchase totals =	$923.07		$999.0540	$999.05	$999.05	$999.00