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	$72.47	12.196%	$81.3084	$81.31	$81.30	$81.30
Purchase #2	$180.57	13.655%	$205.2268	$205.23	$205.25	$205.20
Purchase #3	$80.37	6.506%	$85.5989	$85.60	$85.60	$85.60
Purchase #4	$189.27	10.696%	$209.5143	$209.51	$209.50	$209.50
Purchase #5	$163.83	9.263%	$179.0056	$179.01	$179.00	$179.00
Purchase #6	$83.78	6.245%	$89.0121	$89.01	$89.00	$89.00
Purchase #7	$152.69	10.741%	$169.0904	$169.09	$169.10	$169.10
7 purchase totals =	$922.98		$1,018.7565	$1,018.76	$1,018.75	$1,018.70