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	$46.49	9.503%	$50.9079	$50.91	$50.90	$50.90
Purchase #2	$73.82	13.786%	$83.9968	$84.00	$84.00	$84.00
Purchase #3	$210.40	10.491%	$232.4731	$232.47	$232.45	$232.50
Purchase #4	$167.47	13.818%	$190.611	$190.61	$190.60	$190.60
Purchase #5	$27.39	7.212%	$29.3654	$29.37	$29.35	$29.40
Purchase #6	$52.73	7.428%	$56.6468	$56.65	$56.65	$56.60
Purchase #7	$85.48	5.166%	$89.8959	$89.90	$89.90	$89.90
7 purchase totals =	$663.78		$733.8969	$733.91	$733.85	$733.90