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	$70.39	10.582%	$77.8387	$77.84	$77.85	$77.80
Purchase #2	$178.37	12.460%	$200.5949	$200.59	$200.60	$200.60
Purchase #3	$114.54	3.691%	$118.7677	$118.77	$118.75	$118.80
Purchase #4	$203.62	9.450%	$222.8621	$222.86	$222.85	$222.90
Purchase #5	$147.97	9.511%	$162.0434	$162.04	$162.05	$162.00
Purchase #6	$7.96	10.207%	$8.7725	$8.77	$8.75	$8.80
Purchase #7	$238.74	13.104%	$270.0245	$270.02	$270.00	$270.00
7 purchase totals =	$961.59		$1,060.9038	$1,060.89	$1,060.85	$1,060.90