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	$105.81	11.137%	$117.5941	$117.59	$117.60	$117.60
Purchase #2	$94.38	6.331%	$100.3552	$100.36	$100.35	$100.40
Purchase #3	$161.80	11.200%	$179.9216	$179.92	$179.90	$179.90
Purchase #4	$233.56	7.265%	$250.5281	$250.53	$250.55	$250.50
Purchase #5	$47.63	12.788%	$53.7209	$53.72	$53.70	$53.70
Purchase #6	$166.94	9.582%	$182.9362	$182.94	$182.95	$182.90
Purchase #7	$189.90	6.589%	$202.4125	$202.41	$202.40	$202.40
7 purchase totals =	$1,000.02		$1,087.4686	$1,087.47	$1,087.45	$1,087.40