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	$174.84	6.596%	$186.3724	$186.37	$186.35	$186.40
Purchase #2	$180.62	13.423%	$204.8646	$204.86	$204.85	$204.90
Purchase #3	$122.90	3.577%	$127.2961	$127.30	$127.30	$127.30
Purchase #4	$69.56	4.722%	$72.8446	$72.84	$72.85	$72.80
Purchase #5	$160.80	7.223%	$172.4146	$172.41	$172.40	$172.40
Purchase #6	$154.28	7.754%	$166.2429	$166.24	$166.25	$166.20
Purchase #7	$227.57	9.510%	$249.2119	$249.21	$249.20	$249.20
7 purchase totals =	$1,090.57		$1,179.2471	$1,179.23	$1,179.20	$1,179.20