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	$150.40	9.729%	$165.0324	$165.03	$165.05	$165.00
Purchase #2	$100.91	8.294%	$109.2795	$109.28	$109.30	$109.30
Purchase #3	$244.64	10.728%	$270.885	$270.89	$270.90	$270.90
Purchase #4	$122.73	11.153%	$136.4181	$136.42	$136.40	$136.40
Purchase #5	$180.82	8.859%	$196.8388	$196.84	$196.85	$196.80
Purchase #6	$40.95	7.119%	$43.8652	$43.87	$43.85	$43.90
Purchase #7	$163.46	4.172%	$170.2796	$170.28	$170.30	$170.30
7 purchase totals =	$1,003.91		$1,092.5986	$1,092.61	$1,092.65	$1,092.60