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	$27.97	13.454%	$31.7331	$31.73	$31.75	$31.70
Purchase #2	$204.79	6.821%	$218.7587	$218.76	$218.75	$218.80
Purchase #3	$231.26	13.774%	$263.1138	$263.11	$263.10	$263.10
Purchase #4	$82.88	9.616%	$90.8497	$90.85	$90.85	$90.80
Purchase #5	$139.39	10.236%	$153.658	$153.66	$153.65	$153.70
Purchase #6	$186.57	5.315%	$196.4862	$196.49	$196.50	$196.50
Purchase #7	$217.65	7.673%	$234.3503	$234.35	$234.35	$234.40
7 purchase totals =	$1,090.51		$1,188.9498	$1,188.95	$1,188.95	$1,189.00