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	$250.54	10.618%	$277.1423	$277.14	$277.15	$277.10
Purchase #2	$80.39	7.162%	$86.1475	$86.15	$86.15	$86.10
Purchase #3	$73.48	11.716%	$82.0889	$82.09	$82.10	$82.10
Purchase #4	$74.32	8.316%	$80.5005	$80.50	$80.50	$80.50
Purchase #5	$25.96	6.626%	$27.6801	$27.68	$27.70	$27.70
Purchase #6	$154.56	10.786%	$171.2308	$171.23	$171.25	$171.20
Purchase #7	$194.53	10.402%	$214.765	$214.77	$214.75	$214.80
7 purchase totals =	$853.78		$939.5551	$939.56	$939.60	$939.50