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	$84.92	6.649%	$90.5663	$90.57	$90.55	$90.60
Purchase #2	$174.36	6.234%	$185.2296	$185.23	$185.25	$185.20
Purchase #3	$232.56	10.782%	$257.6346	$257.63	$257.65	$257.60
Purchase #4	$57.58	7.522%	$61.9112	$61.91	$61.90	$61.90
Purchase #5	$213.43	5.126%	$224.3704	$224.37	$224.35	$224.40
Purchase #6	$28.59	10.271%	$31.5265	$31.53	$31.55	$31.50
Purchase #7	$144.83	9.755%	$158.9582	$158.96	$158.95	$159.00
7 purchase totals =	$936.27		$1,010.1968	$1,010.20	$1,010.20	$1,010.20