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	$158.65	12.395%	$178.3147	$178.31	$178.30	$178.30
Purchase #2	$90.48	7.695%	$97.4424	$97.44	$97.45	$97.40
Purchase #3	$31.73	11.481%	$35.3729	$35.37	$35.35	$35.40
Purchase #4	$96.45	8.220%	$104.3782	$104.38	$104.40	$104.40
Purchase #5	$27.89	3.767%	$28.9406	$28.94	$28.95	$28.90
Purchase #6	$58.77	4.855%	$61.6233	$61.62	$61.60	$61.60
Purchase #7	$28.81	12.449%	$32.3966	$32.40	$32.40	$32.40
7 purchase totals =	$492.78		$538.4687	$538.46	$538.45	$538.40