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	$18.25	12.601%	$20.5497	$20.55	$20.55	$20.50
Purchase #2	$193.87	6.703%	$206.8651	$206.87	$206.85	$206.90
Purchase #3	$220.59	13.500%	$250.3697	$250.37	$250.35	$250.40
Purchase #4	$178.67	5.645%	$188.7559	$188.76	$188.75	$188.80
Purchase #5	$113.71	4.170%	$118.4517	$118.45	$118.45	$118.50
Purchase #6	$71.34	8.322%	$77.2769	$77.28	$77.30	$77.30
Purchase #7	$123.94	13.730%	$140.957	$140.96	$140.95	$141.00
7 purchase totals =	$920.37		$1,003.2260	$1,003.24	$1,003.20	$1,003.40