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	$27.77	11.142%	$30.8641	$30.86	$30.85	$30.90
Purchase #2	$225.34	11.106%	$250.3663	$250.37	$250.35	$250.40
Purchase #3	$126.84	9.638%	$139.0648	$139.06	$139.05	$139.10
Purchase #4	$7.78	9.674%	$8.5326	$8.53	$8.55	$8.50
Purchase #5	$182.38	4.443%	$190.4831	$190.48	$190.50	$190.50
Purchase #6	$170.53	8.503%	$185.0302	$185.03	$185.05	$185.00
Purchase #7	$122.51	7.266%	$131.4116	$131.41	$131.40	$131.40
7 purchase totals =	$863.15		$935.7527	$935.74	$935.75	$935.80