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	$100.35	10.391%	$110.7774	$110.78	$110.80	$110.80
Purchase #2	$188.28	12.641%	$212.0805	$212.08	$212.10	$212.10
Purchase #3	$119.55	3.666%	$123.9327	$123.93	$123.95	$123.90
Purchase #4	$153.73	13.674%	$174.751	$174.75	$174.75	$174.80
Purchase #5	$99.36	10.618%	$109.91	$109.91	$109.90	$109.90
Purchase #6	$133.85	9.372%	$146.3944	$146.39	$146.40	$146.40
Purchase #7	$99.54	5.822%	$105.3352	$105.34	$105.35	$105.30
7 purchase totals =	$894.66		$983.1812	$983.18	$983.25	$983.20