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	$25.90	11.436%	$28.8619	$28.86	$28.85	$28.90
Purchase #2	$152.55	9.360%	$166.8287	$166.83	$166.85	$166.80
Purchase #3	$86.79	4.135%	$90.3788	$90.38	$90.40	$90.40
Purchase #4	$206.90	10.306%	$228.2231	$228.22	$228.20	$228.20
Purchase #5	$105.84	3.281%	$109.3126	$109.31	$109.30	$109.30
Purchase #6	$136.87	13.474%	$155.3119	$155.31	$155.30	$155.30
Purchase #7	$160.42	9.856%	$176.231	$176.23	$176.25	$176.20
7 purchase totals =	$875.27		$955.1480	$955.14	$955.15	$955.10