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	$185.29	6.198%	$196.7743	$196.77	$196.75	$196.80
Purchase #2	$168.33	10.382%	$185.806	$185.81	$185.80	$185.80
Purchase #3	$125.86	11.597%	$140.456	$140.46	$140.45	$140.50
Purchase #4	$207.83	5.574%	$219.4144	$219.41	$219.40	$219.40
Purchase #5	$167.61	8.206%	$181.3641	$181.36	$181.35	$181.40
Purchase #6	$9.58	9.343%	$10.4751	$10.48	$10.50	$10.50
Purchase #7	$128.81	12.270%	$144.615	$144.62	$144.60	$144.60
7 purchase totals =	$993.31		$1,078.9049	$1,078.91	$1,078.85	$1,079.00