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	$188.32	13.169%	$213.1199	$213.12	$213.10	$213.10
Purchase #2	$209.91	9.398%	$229.6373	$229.64	$229.65	$229.60
Purchase #3	$96.60	3.800%	$100.2708	$100.27	$100.25	$100.30
Purchase #4	$115.81	10.427%	$127.8855	$127.89	$127.90	$127.90
Purchase #5	$60.38	12.694%	$68.0446	$68.04	$68.05	$68.00
Purchase #6	$162.42	5.402%	$171.1939	$171.19	$171.20	$171.20
Purchase #7	$231.40	10.582%	$255.8867	$255.89	$255.90	$255.90
7 purchase totals =	$1,064.84		$1,166.0387	$1,166.04	$1,166.05	$1,166.00