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	$78.33	5.281%	$82.4666	$82.47	$82.45	$82.50
Purchase #2	$138.79	3.272%	$143.3312	$143.33	$143.35	$143.30
Purchase #3	$81.38	11.812%	$90.9926	$90.99	$91.00	$91.00
Purchase #4	$134.61	7.821%	$145.1378	$145.14	$145.15	$145.10
Purchase #5	$137.55	7.220%	$147.4811	$147.48	$147.50	$147.50
Purchase #6	$93.98	4.689%	$98.3867	$98.39	$98.40	$98.40
Purchase #7	$106.64	11.322%	$118.7138	$118.71	$118.70	$118.70
7 purchase totals =	$771.28		$826.5098	$826.51	$826.55	$826.50