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	$39.47	3.610%	$40.8949	$40.89	$40.90	$40.90
Purchase #2	$56.37	5.344%	$59.3824	$59.38	$59.40	$59.40
Purchase #3	$225.30	12.737%	$253.9965	$254.00	$254.00	$254.00
Purchase #4	$59.44	3.730%	$61.6571	$61.66	$61.65	$61.70
Purchase #5	$140.69	6.583%	$149.9516	$149.95	$149.95	$150.00
Purchase #6	$245.84	13.400%	$278.7826	$278.78	$278.80	$278.80
Purchase #7	$150.93	9.496%	$165.2623	$165.26	$165.25	$165.30
7 purchase totals =	$918.04		$1,009.9274	$1,009.92	$1,009.95	$1,010.10