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	$215.29	13.124%	$243.5447	$243.54	$243.55	$243.50
Purchase #2	$218.35	9.368%	$238.805	$238.81	$238.80	$238.80
Purchase #3	$81.26	10.370%	$89.6867	$89.69	$89.70	$89.70
Purchase #4	$157.98	6.773%	$168.68	$168.68	$168.70	$168.70
Purchase #5	$89.56	11.553%	$99.9069	$99.91	$99.90	$99.90
Purchase #6	$145.56	6.793%	$155.4479	$155.45	$155.45	$155.40
Purchase #7	$57.61	6.771%	$61.5108	$61.51	$61.50	$61.50
7 purchase totals =	$965.61		$1,057.5820	$1,057.59	$1,057.60	$1,057.50