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	$250.92	9.438%	$274.6018	$274.60	$274.60	$274.60
Purchase #2	$31.54	6.143%	$33.4775	$33.48	$33.50	$33.50
Purchase #3	$43.63	8.459%	$47.3207	$47.32	$47.30	$47.30
Purchase #4	$151.85	9.695%	$166.5719	$166.57	$166.55	$166.60
Purchase #5	$29.73	7.696%	$32.018	$32.02	$32.00	$32.00
Purchase #6	$69.38	11.766%	$77.5433	$77.54	$77.55	$77.50
Purchase #7	$93.56	4.635%	$97.8965	$97.90	$97.90	$97.90
7 purchase totals =	$670.61		$729.4297	$729.43	$729.40	$729.40