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	$9.43	10.711%	$10.44	$10.44	$10.45	$10.40
Purchase #2	$93.99	11.188%	$104.5056	$104.51	$104.50	$104.50
Purchase #3	$102.36	6.746%	$109.2652	$109.27	$109.25	$109.30
Purchase #4	$243.62	10.574%	$269.3804	$269.38	$269.40	$269.40
Purchase #5	$159.63	4.218%	$166.3632	$166.36	$166.35	$166.40
Purchase #6	$75.51	9.299%	$82.5317	$82.53	$82.55	$82.50
Purchase #7	$69.51	11.809%	$77.7184	$77.72	$77.70	$77.70
7 purchase totals =	$754.05		$820.2045	$820.21	$820.20	$820.20