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	$77.73	3.369%	$80.3487	$80.35	$80.35	$80.30
Purchase #2	$87.29	12.846%	$98.5033	$98.50	$98.50	$98.50
Purchase #3	$191.80	6.685%	$204.6218	$204.62	$204.60	$204.60
Purchase #4	$49.81	10.389%	$54.9848	$54.98	$55.00	$55.00
Purchase #5	$32.85	10.663%	$36.3528	$36.35	$36.35	$36.40
Purchase #6	$97.96	8.699%	$106.4815	$106.48	$106.50	$106.50
Purchase #7	$187.59	4.650%	$196.3129	$196.31	$196.30	$196.30
7 purchase totals =	$725.03		$777.6058	$777.59	$777.60	$777.60