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	$245.91	3.166%	$253.6955	$253.70	$253.70	$253.70
Purchase #2	$140.48	11.464%	$156.5846	$156.58	$156.60	$156.60
Purchase #3	$231.80	9.723%	$254.3379	$254.34	$254.35	$254.30
Purchase #4	$128.99	5.865%	$136.5553	$136.56	$136.55	$136.60
Purchase #5	$105.37	7.503%	$113.2759	$113.28	$113.30	$113.30
Purchase #6	$124.50	9.604%	$136.457	$136.46	$136.45	$136.50
Purchase #7	$156.42	9.623%	$171.4723	$171.47	$171.45	$171.50
7 purchase totals =	$1,133.47		$1,222.3785	$1,222.39	$1,222.40	$1,222.50