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	$28.34	12.131%	$31.7779	$31.78	$31.80	$31.80
Purchase #2	$245.65	11.717%	$274.4328	$274.43	$274.45	$274.40
Purchase #3	$81.72	9.176%	$89.2186	$89.22	$89.20	$89.20
Purchase #4	$74.67	7.479%	$80.2546	$80.25	$80.25	$80.30
Purchase #5	$235.69	10.280%	$259.9189	$259.92	$259.90	$259.90
Purchase #6	$193.71	10.399%	$213.8539	$213.85	$213.85	$213.90
Purchase #7	$61.84	9.845%	$67.9281	$67.93	$67.95	$67.90
7 purchase totals =	$921.62		$1,017.3848	$1,017.38	$1,017.40	$1,017.40