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	$83.61	7.600%	$89.9644	$89.96	$89.95	$90.00
Purchase #2	$242.28	13.631%	$275.3052	$275.31	$275.30	$275.30
Purchase #3	$110.81	6.413%	$117.9162	$117.92	$117.90	$117.90
Purchase #4	$210.55	3.342%	$217.5866	$217.59	$217.60	$217.60
Purchase #5	$89.57	13.856%	$101.9808	$101.98	$102.00	$102.00
Purchase #6	$209.87	12.754%	$236.6368	$236.64	$236.65	$236.60
Purchase #7	$71.70	10.366%	$79.1324	$79.13	$79.15	$79.10
7 purchase totals =	$1,018.39		$1,118.5224	$1,118.53	$1,118.55	$1,118.50