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	$100.38	3.564%	$103.9575	$103.96	$103.95	$104.00
Purchase #2	$33.89	9.489%	$37.1058	$37.11	$37.10	$37.10
Purchase #3	$118.36	7.740%	$127.5211	$127.52	$127.50	$127.50
Purchase #4	$202.65	12.108%	$227.1869	$227.19	$227.20	$227.20
Purchase #5	$215.77	7.423%	$231.7866	$231.79	$231.80	$231.80
Purchase #6	$23.53	3.819%	$24.4286	$24.43	$24.45	$24.40
Purchase #7	$151.32	9.139%	$165.1491	$165.15	$165.15	$165.10
7 purchase totals =	$845.90		$917.1356	$917.15	$917.15	$917.10