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	$99.86	4.354%	$104.2079	$104.21	$104.20	$104.20
Purchase #2	$30.72	9.520%	$33.6445	$33.64	$33.65	$33.60
Purchase #3	$152.97	12.713%	$172.4171	$172.42	$172.40	$172.40
Purchase #4	$116.70	7.499%	$125.4513	$125.45	$125.45	$125.50
Purchase #5	$242.63	10.611%	$268.3755	$268.38	$268.40	$268.40
Purchase #6	$79.34	9.169%	$86.6147	$86.61	$86.60	$86.60
Purchase #7	$82.56	5.316%	$86.9489	$86.95	$86.95	$86.90
7 purchase totals =	$804.78		$877.6599	$877.66	$877.65	$877.60