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	$150.50	11.223%	$167.3906	$167.39	$167.40	$167.40
Purchase #2	$247.56	9.315%	$270.6202	$270.62	$270.60	$270.60
Purchase #3	$31.73	3.418%	$32.8145	$32.81	$32.80	$32.80
Purchase #4	$205.27	8.714%	$223.1572	$223.16	$223.15	$223.20
Purchase #5	$28.53	13.717%	$32.4435	$32.44	$32.45	$32.40
Purchase #6	$167.65	7.489%	$180.2053	$180.21	$180.20	$180.20
Purchase #7	$233.34	6.727%	$249.0368	$249.04	$249.05	$249.00
7 purchase totals =	$1,064.58		$1,155.6681	$1,155.67	$1,155.65	$1,155.60