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	$198.42	11.464%	$221.1669	$221.17	$221.15	$221.20
Purchase #2	$225.38	13.505%	$255.8176	$255.82	$255.80	$255.80
Purchase #3	$85.99	5.685%	$90.8785	$90.88	$90.90	$90.90
Purchase #4	$196.56	3.168%	$202.787	$202.79	$202.80	$202.80
Purchase #5	$55.48	7.722%	$59.7642	$59.76	$59.75	$59.80
Purchase #6	$34.44	9.819%	$37.8217	$37.82	$37.80	$37.80
Purchase #7	$14.52	3.740%	$15.063	$15.06	$15.05	$15.10
7 purchase totals =	$810.79		$883.2989	$883.30	$883.25	$883.40