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	$7.86	12.863%	$8.871	$8.87	$8.85	$8.90
Purchase #2	$131.86	11.155%	$146.569	$146.57	$146.55	$146.60
Purchase #3	$104.99	7.780%	$113.1582	$113.16	$113.15	$113.20
Purchase #4	$222.67	9.353%	$243.4963	$243.50	$243.50	$243.50
Purchase #5	$111.52	3.712%	$115.6596	$115.66	$115.65	$115.70
Purchase #6	$96.45	3.512%	$99.8373	$99.84	$99.85	$99.80
Purchase #7	$37.82	11.520%	$42.1769	$42.18	$42.20	$42.20
7 purchase totals =	$713.17		$769.7683	$769.78	$769.75	$769.90