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	$241.46	13.255%	$273.4655	$273.47	$273.45	$273.50
Purchase #2	$234.56	9.827%	$257.6102	$257.61	$257.60	$257.60
Purchase #3	$165.63	8.417%	$179.5711	$179.57	$179.55	$179.60
Purchase #4	$79.58	12.244%	$89.3238	$89.32	$89.30	$89.30
Purchase #5	$34.75	13.261%	$39.3582	$39.36	$39.35	$39.40
Purchase #6	$31.87	9.829%	$35.0025	$35.00	$35.00	$35.00
Purchase #7	$61.45	9.624%	$67.3639	$67.36	$67.35	$67.40
7 purchase totals =	$849.30		$941.6952	$941.69	$941.60	$941.80