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	$83.91	6.516%	$89.3776	$89.38	$89.40	$89.40
Purchase #2	$36.53	13.175%	$41.3428	$41.34	$41.35	$41.30
Purchase #3	$131.45	5.250%	$138.3511	$138.35	$138.35	$138.40
Purchase #4	$59.98	6.412%	$63.8259	$63.83	$63.85	$63.80
Purchase #5	$106.26	10.359%	$117.2675	$117.27	$117.25	$117.30
Purchase #6	$211.65	9.567%	$231.8986	$231.90	$231.90	$231.90
Purchase #7	$200.74	6.254%	$213.2943	$213.29	$213.30	$213.30
7 purchase totals =	$830.52		$895.3578	$895.36	$895.40	$895.40