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	$88.78	11.401%	$98.9018	$98.90	$98.90	$98.90
Purchase #2	$139.94	11.857%	$156.5327	$156.53	$156.55	$156.50
Purchase #3	$59.70	7.623%	$64.2509	$64.25	$64.25	$64.30
Purchase #4	$37.46	8.817%	$40.7628	$40.76	$40.75	$40.80
Purchase #5	$45.74	3.539%	$47.3587	$47.36	$47.35	$47.40
Purchase #6	$55.93	9.484%	$61.2344	$61.23	$61.25	$61.20
Purchase #7	$223.78	13.230%	$253.3861	$253.39	$253.40	$253.40
7 purchase totals =	$651.33		$722.4274	$722.42	$722.45	$722.50