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	$121.28	7.738%	$130.6646	$130.66	$130.65	$130.70
Purchase #2	$180.31	11.220%	$200.5408	$200.54	$200.55	$200.50
Purchase #3	$229.48	6.743%	$244.9538	$244.95	$244.95	$245.00
Purchase #4	$48.88	4.710%	$51.1822	$51.18	$51.20	$51.20
Purchase #5	$39.78	6.734%	$42.4588	$42.46	$42.45	$42.50
Purchase #6	$38.55	10.200%	$42.4821	$42.48	$42.50	$42.50
Purchase #7	$69.83	12.403%	$78.491	$78.49	$78.50	$78.50
7 purchase totals =	$728.11		$790.7733	$790.76	$790.80	$790.90