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	$31.69	5.619%	$33.4707	$33.47	$33.45	$33.50
Purchase #2	$73.84	11.218%	$82.1234	$82.12	$82.10	$82.10
Purchase #3	$83.27	9.125%	$90.8684	$90.87	$90.85	$90.90
Purchase #4	$30.83	4.435%	$32.1973	$32.20	$32.20	$32.20
Purchase #5	$192.49	11.772%	$215.1499	$215.15	$215.15	$215.10
Purchase #6	$216.36	9.837%	$237.6433	$237.64	$237.65	$237.60
Purchase #7	$227.39	8.674%	$247.1138	$247.11	$247.10	$247.10
7 purchase totals =	$855.87		$938.5668	$938.56	$938.50	$938.50