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	$199.69	12.404%	$224.4595	$224.46	$224.45	$224.50
Purchase #2	$169.77	6.491%	$180.7898	$180.79	$180.80	$180.80
Purchase #3	$172.95	4.448%	$180.6428	$180.64	$180.65	$180.60
Purchase #4	$29.63	12.277%	$33.2677	$33.27	$33.25	$33.30
Purchase #5	$248.96	5.774%	$263.335	$263.34	$263.35	$263.30
Purchase #6	$88.94	6.424%	$94.6535	$94.65	$94.65	$94.70
Purchase #7	$90.48	11.372%	$100.7694	$100.77	$100.75	$100.80
7 purchase totals =	$1,000.42		$1,077.9177	$1,077.92	$1,077.90	$1,078.00