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	$37.88	12.299%	$42.5389	$42.54	$42.55	$42.50
Purchase #2	$159.79	5.542%	$168.6456	$168.65	$168.65	$168.60
Purchase #3	$245.28	3.502%	$253.8697	$253.87	$253.85	$253.90
Purchase #4	$41.41	10.240%	$45.6504	$45.65	$45.65	$45.70
Purchase #5	$122.77	12.803%	$138.4882	$138.49	$138.50	$138.50
Purchase #6	$182.32	12.389%	$204.9076	$204.91	$204.90	$204.90
Purchase #7	$209.35	8.196%	$226.5083	$226.51	$226.50	$226.50
7 purchase totals =	$998.80		$1,080.6087	$1,080.62	$1,080.60	$1,080.60