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	$37.96	7.734%	$40.8958	$40.90	$40.90	$40.90
Purchase #2	$99.31	5.509%	$104.781	$104.78	$104.80	$104.80
Purchase #3	$166.69	5.608%	$176.038	$176.04	$176.05	$176.00
Purchase #4	$67.98	7.772%	$73.2634	$73.26	$73.25	$73.30
Purchase #5	$215.76	11.266%	$240.0675	$240.07	$240.05	$240.10
Purchase #6	$195.53	13.747%	$222.4095	$222.41	$222.40	$222.40
Purchase #7	$79.32	11.338%	$88.3133	$88.31	$88.30	$88.30
7 purchase totals =	$862.55		$945.7685	$945.77	$945.75	$945.80