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	$215.48	11.526%	$240.3162	$240.32	$240.30	$240.30
Purchase #2	$12.86	4.526%	$13.442	$13.44	$13.45	$13.40
Purchase #3	$90.75	10.620%	$100.3877	$100.39	$100.40	$100.40
Purchase #4	$133.34	5.702%	$140.943	$140.94	$140.95	$140.90
Purchase #5	$232.69	11.375%	$259.1585	$259.16	$259.15	$259.20
Purchase #6	$236.34	11.781%	$264.1832	$264.18	$264.20	$264.20
Purchase #7	$41.33	8.223%	$44.7286	$44.73	$44.75	$44.70
7 purchase totals =	$962.79		$1,063.1592	$1,063.16	$1,063.20	$1,063.10