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	$25.89	8.872%	$28.187	$28.19	$28.20	$28.20
Purchase #2	$195.55	10.471%	$216.026	$216.03	$216.05	$216.00
Purchase #3	$189.98	5.663%	$200.7386	$200.74	$200.75	$200.70
Purchase #4	$196.69	6.682%	$209.8328	$209.83	$209.85	$209.80
Purchase #5	$79.73	13.509%	$90.5007	$90.50	$90.50	$90.50
Purchase #6	$121.72	5.206%	$128.0567	$128.06	$128.05	$128.10
Purchase #7	$220.59	3.600%	$228.5312	$228.53	$228.55	$228.50
7 purchase totals =	$1,030.15		$1,101.8730	$1,101.88	$1,101.95	$1,101.80