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	$69.64	12.453%	$78.3123	$78.31	$78.30	$78.30
Purchase #2	$38.81	7.788%	$41.8325	$41.83	$41.85	$41.80
Purchase #3	$167.43	8.572%	$181.7821	$181.78	$181.80	$181.80
Purchase #4	$247.37	12.813%	$279.0655	$279.07	$279.05	$279.10
Purchase #5	$168.72	13.533%	$191.5529	$191.55	$191.55	$191.60
Purchase #6	$37.73	9.656%	$41.3732	$41.37	$41.35	$41.40
Purchase #7	$201.52	11.648%	$224.993	$224.99	$225.00	$225.00
7 purchase totals =	$931.22		$1,038.9115	$1,038.90	$1,038.90	$1,039.00