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	$174.87	4.649%	$182.9997	$183.00	$183.00	$183.00
Purchase #2	$232.45	3.420%	$240.3998	$240.40	$240.40	$240.40
Purchase #3	$185.84	5.695%	$196.4236	$196.42	$196.40	$196.40
Purchase #4	$72.46	3.334%	$74.8758	$74.88	$74.90	$74.90
Purchase #5	$55.55	10.387%	$61.32	$61.32	$61.30	$61.30
Purchase #6	$38.51	7.302%	$41.322	$41.32	$41.30	$41.30
Purchase #7	$78.77	3.700%	$81.6845	$81.68	$81.70	$81.70
7 purchase totals =	$838.45		$879.0254	$879.02	$879.00	$879.00