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	$74.80	10.291%	$82.4977	$82.50	$82.50	$82.50
Purchase #2	$90.69	3.130%	$93.5286	$93.53	$93.55	$93.50
Purchase #3	$35.75	5.306%	$37.6469	$37.65	$37.65	$37.60
Purchase #4	$19.69	8.555%	$21.3745	$21.37	$21.35	$21.40
Purchase #5	$125.27	12.212%	$140.568	$140.57	$140.55	$140.60
Purchase #6	$142.33	12.372%	$159.9391	$159.94	$159.95	$159.90
Purchase #7	$246.25	9.179%	$268.8533	$268.85	$268.85	$268.90
7 purchase totals =	$734.78		$804.4081	$804.41	$804.40	$804.40