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	$51.90	3.111%	$53.5146	$53.51	$53.50	$53.50
Purchase #2	$48.90	3.738%	$50.7279	$50.73	$50.75	$50.70
Purchase #3	$128.48	7.451%	$138.053	$138.05	$138.05	$138.10
Purchase #4	$149.84	12.322%	$168.3033	$168.30	$168.30	$168.30
Purchase #5	$86.82	3.142%	$89.5479	$89.55	$89.55	$89.50
Purchase #6	$133.68	8.645%	$145.2366	$145.24	$145.25	$145.20
Purchase #7	$193.59	8.197%	$209.4586	$209.46	$209.45	$209.50
7 purchase totals =	$793.21		$854.8419	$854.84	$854.85	$854.80