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	$39.52	5.568%	$41.7205	$41.72	$41.70	$41.70
Purchase #2	$169.42	13.484%	$192.2646	$192.26	$192.25	$192.30
Purchase #3	$91.98	10.146%	$101.3123	$101.31	$101.30	$101.30
Purchase #4	$32.79	3.242%	$33.8531	$33.85	$33.85	$33.90
Purchase #5	$29.72	12.555%	$33.4513	$33.45	$33.45	$33.50
Purchase #6	$92.65	11.539%	$103.3409	$103.34	$103.35	$103.30
Purchase #7	$180.57	10.611%	$199.7303	$199.73	$199.75	$199.70
7 purchase totals =	$636.65		$705.6730	$705.66	$705.65	$705.70