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	$77.36	3.719%	$80.237	$80.24	$80.25	$80.20
Purchase #2	$214.48	4.382%	$223.8785	$223.88	$223.90	$223.90
Purchase #3	$118.81	10.649%	$131.4621	$131.46	$131.45	$131.50
Purchase #4	$240.58	9.661%	$263.8224	$263.82	$263.80	$263.80
Purchase #5	$165.44	10.841%	$183.3754	$183.38	$183.40	$183.40
Purchase #6	$245.39	3.149%	$253.1173	$253.12	$253.10	$253.10
Purchase #7	$181.27	12.300%	$203.5662	$203.57	$203.55	$203.60
7 purchase totals =	$1,243.33		$1,339.4589	$1,339.47	$1,339.45	$1,339.50