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	$82.33	10.347%	$90.8487	$90.85	$90.85	$90.80
Purchase #2	$176.72	12.218%	$198.3116	$198.31	$198.30	$198.30
Purchase #3	$78.53	11.578%	$87.6222	$87.62	$87.60	$87.60
Purchase #4	$156.56	7.569%	$168.41	$168.41	$168.40	$168.40
Purchase #5	$180.25	8.154%	$194.9476	$194.95	$194.95	$194.90
Purchase #6	$197.63	9.573%	$216.5491	$216.55	$216.55	$216.50
Purchase #7	$29.75	7.562%	$31.9997	$32.00	$32.00	$32.00
7 purchase totals =	$901.77		$988.6889	$988.69	$988.65	$988.50