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	$96.35	8.457%	$104.4983	$104.50	$104.50	$104.50
Purchase #2	$72.57	3.430%	$75.0592	$75.06	$75.05	$75.10
Purchase #3	$71.67	10.170%	$78.9588	$78.96	$78.95	$79.00
Purchase #4	$241.91	8.609%	$262.736	$262.74	$262.75	$262.70
Purchase #5	$130.45	12.333%	$146.5384	$146.54	$146.55	$146.50
Purchase #6	$165.47	12.242%	$185.7268	$185.73	$185.75	$185.70
Purchase #7	$42.94	6.837%	$45.8758	$45.88	$45.90	$45.90
7 purchase totals =	$821.36		$899.3933	$899.41	$899.45	$899.40