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	$243.88	12.240%	$273.7309	$273.73	$273.75	$273.70
Purchase #2	$146.95	5.143%	$154.5076	$154.51	$154.50	$154.50
Purchase #3	$100.39	11.443%	$111.8776	$111.88	$111.90	$111.90
Purchase #4	$25.97	6.801%	$27.7362	$27.74	$27.75	$27.70
Purchase #5	$147.25	10.211%	$162.2857	$162.29	$162.30	$162.30
Purchase #6	$183.73	11.226%	$204.3555	$204.36	$204.35	$204.40
Purchase #7	$6.67	10.232%	$7.3525	$7.35	$7.35	$7.40
7 purchase totals =	$854.84		$941.8460	$941.86	$941.90	$941.90