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	$121.61	5.520%	$128.3229	$128.32	$128.30	$128.30
Purchase #2	$33.36	4.355%	$34.8128	$34.81	$34.80	$34.80
Purchase #3	$52.65	3.120%	$54.2927	$54.29	$54.30	$54.30
Purchase #4	$35.85	5.571%	$37.8472	$37.85	$37.85	$37.80
Purchase #5	$7.43	5.685%	$7.8524	$7.85	$7.85	$7.90
Purchase #6	$139.82	5.860%	$148.0135	$148.01	$148.00	$148.00
Purchase #7	$204.67	7.431%	$219.879	$219.88	$219.90	$219.90
7 purchase totals =	$595.39		$631.0205	$631.01	$631.00	$631.00