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	$165.88	8.790%	$180.4609	$180.46	$180.45	$180.50
Purchase #2	$239.26	12.347%	$268.8014	$268.80	$268.80	$268.80
Purchase #3	$206.99	4.183%	$215.6484	$215.65	$215.65	$215.60
Purchase #4	$33.28	12.674%	$37.4979	$37.50	$37.50	$37.50
Purchase #5	$147.56	3.269%	$152.3837	$152.38	$152.40	$152.40
Purchase #6	$178.38	6.796%	$190.5027	$190.50	$190.50	$190.50
Purchase #7	$34.52	4.465%	$36.0613	$36.06	$36.05	$36.10
7 purchase totals =	$1,005.87		$1,081.3563	$1,081.35	$1,081.35	$1,081.40