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	$167.50	12.391%	$188.2549	$188.25	$188.25	$188.30
Purchase #2	$72.34	10.604%	$80.0109	$80.01	$80.00	$80.00
Purchase #3	$50.79	12.194%	$56.9833	$56.98	$57.00	$57.00
Purchase #4	$92.42	7.366%	$99.2277	$99.23	$99.25	$99.20
Purchase #5	$198.71	5.618%	$209.8735	$209.87	$209.85	$209.90
Purchase #6	$97.85	6.213%	$103.9294	$103.93	$103.95	$103.90
Purchase #7	$156.78	3.579%	$162.3912	$162.39	$162.40	$162.40
7 purchase totals =	$836.39		$900.6709	$900.66	$900.70	$900.70