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	$85.51	5.551%	$90.2567	$90.26	$90.25	$90.30
Purchase #2	$239.53	12.196%	$268.7431	$268.74	$268.75	$268.70
Purchase #3	$145.92	13.696%	$165.9052	$165.91	$165.90	$165.90
Purchase #4	$216.27	5.264%	$227.6545	$227.65	$227.65	$227.70
Purchase #5	$79.80	7.657%	$85.9103	$85.91	$85.90	$85.90
Purchase #6	$151.37	6.723%	$161.5466	$161.55	$161.55	$161.50
Purchase #7	$38.75	12.685%	$43.6654	$43.67	$43.65	$43.70
7 purchase totals =	$957.15		$1,043.6818	$1,043.69	$1,043.65	$1,043.70