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	$71.86	11.361%	$80.024	$80.02	$80.00	$80.00
Purchase #2	$162.56	13.741%	$184.8974	$184.90	$184.90	$184.90
Purchase #3	$203.72	9.600%	$223.2771	$223.28	$223.30	$223.30
Purchase #4	$192.78	5.156%	$202.7197	$202.72	$202.70	$202.70
Purchase #5	$80.39	3.627%	$83.3057	$83.31	$83.30	$83.30
Purchase #6	$56.50	7.684%	$60.8415	$60.84	$60.85	$60.80
Purchase #7	$191.79	12.278%	$215.338	$215.34	$215.35	$215.30
7 purchase totals =	$959.60		$1,050.4034	$1,050.41	$1,050.40	$1,050.30