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	$28.91	12.356%	$32.4821	$32.48	$32.50	$32.50
Purchase #2	$226.49	3.589%	$234.6187	$234.62	$234.60	$234.60
Purchase #3	$131.54	8.203%	$142.3302	$142.33	$142.35	$142.30
Purchase #4	$78.33	12.793%	$88.3508	$88.35	$88.35	$88.40
Purchase #5	$203.66	5.799%	$215.4702	$215.47	$215.45	$215.50
Purchase #6	$145.79	12.697%	$164.301	$164.30	$164.30	$164.30
Purchase #7	$121.37	8.419%	$131.5881	$131.59	$131.60	$131.60
7 purchase totals =	$936.09		$1,009.1411	$1,009.14	$1,009.15	$1,009.20