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	$72.61	10.603%	$80.3088	$80.31	$80.30	$80.30
Purchase #2	$62.55	8.433%	$67.8248	$67.82	$67.80	$67.80
Purchase #3	$80.90	11.413%	$90.1331	$90.13	$90.15	$90.10
Purchase #4	$26.54	8.744%	$28.8607	$28.86	$28.85	$28.90
Purchase #5	$179.90	5.293%	$189.4221	$189.42	$189.40	$189.40
Purchase #6	$36.83	7.138%	$39.4589	$39.46	$39.45	$39.50
Purchase #7	$36.97	8.682%	$40.1797	$40.18	$40.20	$40.20
7 purchase totals =	$496.30		$536.1881	$536.18	$536.15	$536.20