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	$42.43	7.280%	$45.5189	$45.52	$45.50	$45.50
Purchase #2	$141.38	4.412%	$147.6177	$147.62	$147.60	$147.60
Purchase #3	$89.48	7.446%	$96.1427	$96.14	$96.15	$96.10
Purchase #4	$238.65	7.663%	$256.9377	$256.94	$256.95	$256.90
Purchase #5	$133.56	11.874%	$149.4189	$149.42	$149.40	$149.40
Purchase #6	$86.40	8.266%	$93.5418	$93.54	$93.55	$93.50
Purchase #7	$72.82	8.711%	$79.1634	$79.16	$79.15	$79.20
7 purchase totals =	$804.72		$868.3411	$868.34	$868.30	$868.20