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	$159.53	12.507%	$179.4824	$179.48	$179.50	$179.50
Purchase #2	$172.34	4.846%	$180.6916	$180.69	$180.70	$180.70
Purchase #3	$73.40	5.599%	$77.5097	$77.51	$77.50	$77.50
Purchase #4	$72.78	11.270%	$80.9823	$80.98	$81.00	$81.00
Purchase #5	$83.55	6.617%	$89.0785	$89.08	$89.10	$89.10
Purchase #6	$94.66	9.848%	$103.9821	$103.98	$104.00	$104.00
Purchase #7	$30.74	12.657%	$34.6308	$34.63	$34.65	$34.60
7 purchase totals =	$687.00		$746.3574	$746.35	$746.45	$746.40