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	$172.72	7.816%	$186.2198	$186.22	$186.20	$186.20
Purchase #2	$176.45	3.673%	$182.931	$182.93	$182.95	$182.90
Purchase #3	$120.77	13.715%	$137.3336	$137.33	$137.35	$137.30
Purchase #4	$53.77	10.701%	$59.5239	$59.52	$59.50	$59.50
Purchase #5	$189.46	11.645%	$211.5226	$211.52	$211.50	$211.50
Purchase #6	$22.77	12.676%	$25.6563	$25.66	$25.65	$25.70
Purchase #7	$176.51	4.495%	$184.4441	$184.44	$184.45	$184.40
7 purchase totals =	$912.45		$987.6313	$987.62	$987.60	$987.50