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	$38.65	9.733%	$42.4118	$42.41	$42.40	$42.40
Purchase #2	$122.40	10.686%	$135.4797	$135.48	$135.50	$135.50
Purchase #3	$40.42	12.420%	$45.4402	$45.44	$45.45	$45.40
Purchase #4	$86.77	8.174%	$93.8626	$93.86	$93.85	$93.90
Purchase #5	$67.32	6.217%	$71.5053	$71.51	$71.50	$71.50
Purchase #6	$182.30	7.428%	$195.8412	$195.84	$195.85	$195.80
Purchase #7	$188.86	10.835%	$209.323	$209.32	$209.30	$209.30
7 purchase totals =	$726.72		$793.8638	$793.86	$793.85	$793.80