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	$55.60	7.591%	$59.8206	$59.82	$59.80	$59.80
Purchase #2	$173.71	6.293%	$184.6416	$184.64	$184.65	$184.60
Purchase #3	$191.86	5.726%	$202.8459	$202.85	$202.85	$202.80
Purchase #4	$156.98	10.272%	$173.105	$173.11	$173.10	$173.10
Purchase #5	$68.40	3.179%	$70.5744	$70.57	$70.55	$70.60
Purchase #6	$167.88	10.496%	$185.5007	$185.50	$185.50	$185.50
Purchase #7	$165.59	4.723%	$173.4108	$173.41	$173.40	$173.40
7 purchase totals =	$980.02		$1,049.8990	$1,049.90	$1,049.85	$1,049.80