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	$180.65	4.796%	$189.314	$189.31	$189.30	$189.30
Purchase #2	$83.88	11.609%	$93.6176	$93.62	$93.60	$93.60
Purchase #3	$56.62	7.672%	$60.9639	$60.96	$60.95	$61.00
Purchase #4	$71.78	11.578%	$80.0907	$80.09	$80.10	$80.10
Purchase #5	$96.46	8.407%	$104.5694	$104.57	$104.55	$104.60
Purchase #6	$243.40	13.115%	$275.3219	$275.32	$275.30	$275.30
Purchase #7	$105.39	3.434%	$109.0091	$109.01	$109.00	$109.00
7 purchase totals =	$838.18		$912.8866	$912.88	$912.80	$912.90