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	$90.83	7.654%	$97.7821	$97.78	$97.80	$97.80
Purchase #2	$244.53	12.404%	$274.8615	$274.86	$274.85	$274.90
Purchase #3	$222.57	11.179%	$247.4511	$247.45	$247.45	$247.50
Purchase #4	$231.34	7.767%	$249.3082	$249.31	$249.30	$249.30
Purchase #5	$153.36	3.490%	$158.7123	$158.71	$158.70	$158.70
Purchase #6	$88.37	12.329%	$99.2651	$99.27	$99.25	$99.30
Purchase #7	$11.42	9.190%	$12.4695	$12.47	$12.45	$12.50
7 purchase totals =	$1,042.42		$1,139.8498	$1,139.85	$1,139.80	$1,140.00