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	$89.70	10.832%	$99.4163	$99.42	$99.40	$99.40
Purchase #2	$216.72	12.384%	$243.5586	$243.56	$243.55	$243.60
Purchase #3	$235.47	6.435%	$250.6225	$250.62	$250.60	$250.60
Purchase #4	$217.61	12.745%	$245.3444	$245.34	$245.35	$245.30
Purchase #5	$61.80	11.480%	$68.8946	$68.89	$68.90	$68.90
Purchase #6	$182.80	6.161%	$194.0623	$194.06	$194.05	$194.10
Purchase #7	$91.92	3.295%	$94.9488	$94.95	$94.95	$94.90
7 purchase totals =	$1,096.02		$1,196.8475	$1,196.84	$1,196.80	$1,196.80