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	$26.38	3.157%	$27.2128	$27.21	$27.20	$27.20
Purchase #2	$59.25	8.513%	$64.294	$64.29	$64.30	$64.30
Purchase #3	$161.64	6.731%	$172.52	$172.52	$172.50	$172.50
Purchase #4	$10.66	3.765%	$11.0613	$11.06	$11.05	$11.10
Purchase #5	$121.41	8.340%	$131.5356	$131.54	$131.55	$131.50
Purchase #6	$40.44	4.710%	$42.3447	$42.34	$42.35	$42.30
Purchase #7	$215.38	9.828%	$236.5475	$236.55	$236.55	$236.50
7 purchase totals =	$635.16		$685.5159	$685.51	$685.50	$685.40