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	$19.65	4.130%	$20.4615	$20.46	$20.45	$20.50
Purchase #2	$148.36	8.849%	$161.4884	$161.49	$161.50	$161.50
Purchase #3	$224.72	6.327%	$238.938	$238.94	$238.95	$238.90
Purchase #4	$67.98	4.281%	$70.8902	$70.89	$70.90	$70.90
Purchase #5	$176.54	6.439%	$187.9074	$187.91	$187.90	$187.90
Purchase #6	$52.97	6.369%	$56.3437	$56.34	$56.35	$56.30
Purchase #7	$50.33	9.847%	$55.286	$55.29	$55.30	$55.30
7 purchase totals =	$740.55		$791.3152	$791.32	$791.35	$791.30