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	$165.71	12.659%	$186.6872	$186.69	$186.70	$186.70
Purchase #2	$65.42	3.791%	$67.9001	$67.90	$67.90	$67.90
Purchase #3	$192.51	6.245%	$204.5322	$204.53	$204.55	$204.50
Purchase #4	$178.47	10.302%	$196.856	$196.86	$196.85	$196.90
Purchase #5	$137.30	5.767%	$145.2181	$145.22	$145.20	$145.20
Purchase #6	$27.41	7.705%	$29.5219	$29.52	$29.50	$29.50
Purchase #7	$36.55	12.795%	$41.2266	$41.23	$41.25	$41.20
7 purchase totals =	$803.37		$871.9421	$871.95	$871.95	$871.90