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	$35.35	4.432%	$36.9167	$36.92	$36.90	$36.90
Purchase #2	$88.34	4.654%	$92.4513	$92.45	$92.45	$92.50
Purchase #3	$234.56	6.608%	$250.0597	$250.06	$250.05	$250.10
Purchase #4	$194.79	10.366%	$214.9819	$214.98	$215.00	$215.00
Purchase #5	$129.85	11.460%	$144.7308	$144.73	$144.75	$144.70
Purchase #6	$54.58	13.226%	$61.7988	$61.80	$61.80	$61.80
Purchase #7	$215.54	10.867%	$238.9627	$238.96	$238.95	$239.00
7 purchase totals =	$953.01		$1,039.9019	$1,039.90	$1,039.90	$1,040.00