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	$137.77	13.564%	$156.4571	$156.46	$156.45	$156.50
Purchase #2	$78.33	3.786%	$81.2956	$81.30	$81.30	$81.30
Purchase #3	$191.31	11.215%	$212.7654	$212.77	$212.75	$212.80
Purchase #4	$7.79	4.437%	$8.1356	$8.14	$8.15	$8.10
Purchase #5	$87.72	3.284%	$90.6007	$90.60	$90.60	$90.60
Purchase #6	$97.73	12.718%	$110.1593	$110.16	$110.15	$110.20
Purchase #7	$127.37	11.402%	$141.8927	$141.89	$141.90	$141.90
7 purchase totals =	$728.02		$801.3064	$801.32	$801.30	$801.40