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	$82.82	7.825%	$89.3007	$89.30	$89.30	$89.30
Purchase #2	$167.70	9.805%	$184.143	$184.14	$184.15	$184.10
Purchase #3	$240.25	3.837%	$249.4684	$249.47	$249.45	$249.50
Purchase #4	$149.86	9.828%	$164.5882	$164.59	$164.60	$164.60
Purchase #5	$158.88	3.616%	$164.6251	$164.63	$164.65	$164.60
Purchase #6	$95.39	13.786%	$108.5405	$108.54	$108.55	$108.50
Purchase #7	$148.93	8.281%	$161.2629	$161.26	$161.25	$161.30
7 purchase totals =	$1,043.83		$1,121.9288	$1,121.93	$1,121.95	$1,121.90