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	$250.77	9.173%	$273.7731	$273.77	$273.75	$273.80
Purchase #2	$150.86	12.754%	$170.1007	$170.10	$170.10	$170.10
Purchase #3	$172.28	10.794%	$190.8759	$190.88	$190.90	$190.90
Purchase #4	$213.84	11.612%	$238.6711	$238.67	$238.65	$238.70
Purchase #5	$160.89	10.325%	$177.5019	$177.50	$177.50	$177.50
Purchase #6	$157.59	6.805%	$168.314	$168.31	$168.30	$168.30
Purchase #7	$88.82	11.695%	$99.2075	$99.21	$99.20	$99.20
7 purchase totals =	$1,195.05		$1,318.4442	$1,318.44	$1,318.40	$1,318.50