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	$26.42	4.122%	$27.509	$27.51	$27.50	$27.50
Purchase #2	$51.98	6.282%	$55.2454	$55.25	$55.25	$55.20
Purchase #3	$37.85	12.482%	$42.5744	$42.57	$42.55	$42.60
Purchase #4	$233.73	13.498%	$265.2789	$265.28	$265.30	$265.30
Purchase #5	$26.96	4.808%	$28.2562	$28.26	$28.25	$28.30
Purchase #6	$219.75	8.324%	$238.042	$238.04	$238.05	$238.00
Purchase #7	$89.39	10.567%	$98.8358	$98.84	$98.85	$98.80
7 purchase totals =	$686.08		$755.7417	$755.75	$755.75	$755.70