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	$170.31	8.789%	$185.2785	$185.28	$185.30	$185.30
Purchase #2	$42.75	6.266%	$45.4287	$45.43	$45.45	$45.40
Purchase #3	$80.29	5.871%	$85.0038	$85.00	$85.00	$85.00
Purchase #4	$29.64	12.236%	$33.2668	$33.27	$33.25	$33.30
Purchase #5	$53.48	4.383%	$55.824	$55.82	$55.80	$55.80
Purchase #6	$131.90	3.689%	$136.7658	$136.77	$136.75	$136.80
Purchase #7	$237.83	3.815%	$246.9032	$246.90	$246.90	$246.90
7 purchase totals =	$746.20		$788.4708	$788.47	$788.45	$788.50