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	$29.71	5.772%	$31.4249	$31.42	$31.40	$31.40
Purchase #2	$213.81	5.345%	$225.2381	$225.24	$225.25	$225.20
Purchase #3	$136.82	6.186%	$145.2837	$145.28	$145.30	$145.30
Purchase #4	$231.46	11.131%	$257.2238	$257.22	$257.20	$257.20
Purchase #5	$214.68	13.809%	$244.3252	$244.33	$244.35	$244.30
Purchase #6	$65.41	11.438%	$72.8916	$72.89	$72.90	$72.90
Purchase #7	$109.76	6.741%	$117.1589	$117.16	$117.15	$117.20
7 purchase totals =	$1,001.65		$1,093.5462	$1,093.54	$1,093.55	$1,093.50