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	$170.74	7.167%	$182.9769	$182.98	$183.00	$183.00
Purchase #2	$193.77	12.655%	$218.2916	$218.29	$218.30	$218.30
Purchase #3	$90.92	11.716%	$101.5722	$101.57	$101.55	$101.60
Purchase #4	$39.47	10.360%	$43.5591	$43.56	$43.55	$43.60
Purchase #5	$108.50	3.589%	$112.3941	$112.39	$112.40	$112.40
Purchase #6	$53.80	12.716%	$60.6412	$60.64	$60.65	$60.60
Purchase #7	$53.78	11.445%	$59.9351	$59.94	$59.95	$59.90
7 purchase totals =	$710.98		$779.3702	$779.37	$779.40	$779.40