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	$83.26	11.600%	$92.9182	$92.92	$92.90	$92.90
Purchase #2	$28.64	11.182%	$31.8425	$31.84	$31.85	$31.80
Purchase #3	$154.30	9.636%	$169.1683	$169.17	$169.15	$169.20
Purchase #4	$125.59	11.422%	$139.9349	$139.93	$139.95	$139.90
Purchase #5	$195.46	10.795%	$216.5599	$216.56	$216.55	$216.60
Purchase #6	$102.77	6.405%	$109.3524	$109.35	$109.35	$109.40
Purchase #7	$223.77	3.404%	$231.3871	$231.39	$231.40	$231.40
7 purchase totals =	$913.79		$991.1633	$991.16	$991.15	$991.20