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	$90.48	6.326%	$96.2038	$96.20	$96.20	$96.20
Purchase #2	$141.47	12.262%	$158.8171	$158.82	$158.80	$158.80
Purchase #3	$155.98	6.636%	$166.3308	$166.33	$166.35	$166.30
Purchase #4	$19.35	8.799%	$21.0526	$21.05	$21.05	$21.10
Purchase #5	$85.34	7.704%	$91.9146	$91.91	$91.90	$91.90
Purchase #6	$211.64	12.629%	$238.368	$238.37	$238.35	$238.40
Purchase #7	$147.54	5.349%	$155.4319	$155.43	$155.45	$155.40
7 purchase totals =	$851.80		$928.1188	$928.11	$928.10	$928.10