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	$30.52	4.733%	$31.9645	$31.96	$31.95	$32.00
Purchase #2	$240.94	10.303%	$265.764	$265.76	$265.75	$265.80
Purchase #3	$38.75	7.271%	$41.5675	$41.57	$41.55	$41.60
Purchase #4	$196.59	13.179%	$222.4986	$222.50	$222.50	$222.50
Purchase #5	$178.97	3.816%	$185.7995	$185.80	$185.80	$185.80
Purchase #6	$110.61	5.340%	$116.5166	$116.52	$116.50	$116.50
Purchase #7	$232.30	13.217%	$263.0031	$263.00	$263.00	$263.00
7 purchase totals =	$1,028.68		$1,127.1138	$1,127.11	$1,127.05	$1,127.20