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	$200.86	13.451%	$227.8777	$227.88	$227.90	$227.90
Purchase #2	$35.70	6.167%	$37.9016	$37.90	$37.90	$37.90
Purchase #3	$122.33	11.337%	$136.1986	$136.20	$136.20	$136.20
Purchase #4	$205.76	5.764%	$217.62	$217.62	$217.60	$217.60
Purchase #5	$83.68	9.419%	$91.5618	$91.56	$91.55	$91.60
Purchase #6	$229.71	8.826%	$249.9842	$249.98	$250.00	$250.00
Purchase #7	$38.30	10.197%	$42.2055	$42.21	$42.20	$42.20
7 purchase totals =	$916.34		$1,003.3494	$1,003.35	$1,003.35	$1,003.40