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	$89.58	12.613%	$100.8787	$100.88	$100.90	$100.90
Purchase #2	$212.79	10.316%	$234.7414	$234.74	$234.75	$234.70
Purchase #3	$7.44	4.725%	$7.7915	$7.79	$7.80	$7.80
Purchase #4	$136.54	8.128%	$147.638	$147.64	$147.65	$147.60
Purchase #5	$188.73	10.357%	$208.2768	$208.28	$208.30	$208.30
Purchase #6	$164.64	12.518%	$185.2496	$185.25	$185.25	$185.20
Purchase #7	$183.89	12.169%	$206.2676	$206.27	$206.25	$206.30
7 purchase totals =	$983.61		$1,090.8436	$1,090.85	$1,090.90	$1,090.80