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	$9.73	6.288%	$10.3418	$10.34	$10.35	$10.30
Purchase #2	$58.60	6.809%	$62.5901	$62.59	$62.60	$62.60
Purchase #3	$224.99	5.170%	$236.622	$236.62	$236.60	$236.60
Purchase #4	$82.52	4.270%	$86.0436	$86.04	$86.05	$86.00
Purchase #5	$89.44	12.839%	$100.9232	$100.92	$100.90	$100.90
Purchase #6	$195.64	11.825%	$218.7744	$218.77	$218.75	$218.80
Purchase #7	$72.94	8.260%	$78.9648	$78.96	$78.95	$79.00
7 purchase totals =	$733.86		$794.2599	$794.24	$794.20	$794.20