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	$142.87	8.860%	$155.5283	$155.53	$155.55	$155.50
Purchase #2	$209.72	12.593%	$236.13	$236.13	$236.15	$236.10
Purchase #3	$24.33	11.252%	$27.0676	$27.07	$27.05	$27.10
Purchase #4	$209.63	6.439%	$223.1281	$223.13	$223.15	$223.10
Purchase #5	$65.37	11.353%	$72.7915	$72.79	$72.80	$72.80
Purchase #6	$179.47	5.348%	$189.0681	$189.07	$189.05	$189.10
Purchase #7	$205.25	4.507%	$214.5006	$214.50	$214.50	$214.50
7 purchase totals =	$1,036.64		$1,118.2142	$1,118.22	$1,118.25	$1,118.20