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	$186.78	9.687%	$204.8734	$204.87	$204.85	$204.90
Purchase #2	$36.39	9.167%	$39.7259	$39.73	$39.75	$39.70
Purchase #3	$90.66	4.332%	$94.5874	$94.59	$94.60	$94.60
Purchase #4	$186.32	12.238%	$209.1218	$209.12	$209.10	$209.10
Purchase #5	$31.69	3.741%	$32.8755	$32.88	$32.90	$32.90
Purchase #6	$97.29	9.841%	$106.8643	$106.86	$106.85	$106.90
Purchase #7	$51.39	7.710%	$55.3522	$55.35	$55.35	$55.40
7 purchase totals =	$680.52		$743.4005	$743.40	$743.40	$743.50