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	$99.89	12.681%	$112.5571	$112.56	$112.55	$112.60
Purchase #2	$76.61	11.731%	$85.5971	$85.60	$85.60	$85.60
Purchase #3	$190.28	3.276%	$196.5136	$196.51	$196.50	$196.50
Purchase #4	$142.67	9.139%	$155.7086	$155.71	$155.70	$155.70
Purchase #5	$24.65	11.807%	$27.5604	$27.56	$27.55	$27.60
Purchase #6	$80.70	9.248%	$88.1631	$88.16	$88.15	$88.20
Purchase #7	$211.82	12.272%	$237.8146	$237.81	$237.80	$237.80
7 purchase totals =	$826.62		$903.9145	$903.91	$903.85	$904.00