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	$54.81	8.248%	$59.3307	$59.33	$59.35	$59.30
Purchase #2	$103.41	3.285%	$106.807	$106.81	$106.80	$106.80
Purchase #3	$116.25	6.350%	$123.6319	$123.63	$123.65	$123.60
Purchase #4	$195.32	13.668%	$222.0163	$222.02	$222.00	$222.00
Purchase #5	$115.63	6.788%	$123.479	$123.48	$123.50	$123.50
Purchase #6	$119.83	6.311%	$127.3925	$127.39	$127.40	$127.40
Purchase #7	$114.91	9.111%	$125.3795	$125.38	$125.40	$125.40
7 purchase totals =	$820.16		$888.0369	$888.04	$888.10	$888.00