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	$89.56	10.801%	$99.2334	$99.23	$99.25	$99.20
Purchase #2	$90.94	9.223%	$99.3274	$99.33	$99.35	$99.30
Purchase #3	$121.72	13.269%	$137.871	$137.87	$137.85	$137.90
Purchase #4	$114.35	4.471%	$119.4626	$119.46	$119.45	$119.50
Purchase #5	$250.35	6.618%	$266.9182	$266.92	$266.90	$266.90
Purchase #6	$119.81	4.567%	$125.2817	$125.28	$125.30	$125.30
Purchase #7	$36.47	13.629%	$41.4405	$41.44	$41.45	$41.40
7 purchase totals =	$823.20		$889.5348	$889.53	$889.55	$889.50