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	$230.94	12.253%	$259.2371	$259.24	$259.25	$259.20
Purchase #2	$110.77	11.619%	$123.6404	$123.64	$123.65	$123.60
Purchase #3	$87.39	3.258%	$90.2372	$90.24	$90.25	$90.20
Purchase #4	$71.61	13.102%	$80.9923	$80.99	$81.00	$81.00
Purchase #5	$99.98	4.586%	$104.5651	$104.57	$104.55	$104.60
Purchase #6	$237.87	4.382%	$248.2935	$248.29	$248.30	$248.30
Purchase #7	$211.84	4.578%	$221.538	$221.54	$221.55	$221.50
7 purchase totals =	$1,050.40		$1,128.5036	$1,128.51	$1,128.55	$1,128.40