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	$204.41	10.165%	$225.1883	$225.19	$225.20	$225.20
Purchase #2	$7.54	7.183%	$8.0816	$8.08	$8.10	$8.10
Purchase #3	$38.44	6.119%	$40.7921	$40.79	$40.80	$40.80
Purchase #4	$81.33	10.526%	$89.8908	$89.89	$89.90	$89.90
Purchase #5	$234.31	7.214%	$251.2131	$251.21	$251.20	$251.20
Purchase #6	$32.30	4.609%	$33.7887	$33.79	$33.80	$33.80
Purchase #7	$18.72	8.726%	$20.3535	$20.35	$20.35	$20.40
7 purchase totals =	$617.05		$669.3081	$669.30	$669.35	$669.40